Quarterly report pursuant to Section 13 or 15(d)

Unsecured Line of Credit Payable - Narrative (Details)

v3.10.0.1
Unsecured Line of Credit Payable - Narrative (Details)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
USD ($)
extension_option
Sep. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
Mar. 29, 2018
USD ($)
Sep. 15, 2015
USD ($)
Interest Rate Swap [Member]          
Line of Credit Facility [Line Items]          
Derivative, notional amount $ 400,000,000 $ 400,000,000      
LIBOR [Member]          
Line of Credit Facility [Line Items]          
Debt instrument variable rate (percent) 2.26% 2.26%      
Line of Credit          
Line of Credit Facility [Line Items]          
Commitment fee (percent)   0.20%      
Interest rate during period (percent)   1.00%      
Line of Credit | Minimum [Member]          
Line of Credit Facility [Line Items]          
Commitment fee (percent)   0.10%      
Line of Credit | Maximum [Member]          
Line of Credit Facility [Line Items]          
Commitment fee (percent)   0.30%      
Line of Credit | LIBOR [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   1.00%      
Line of Credit | LIBOR [Member] | Minimum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   0.775%      
Line of Credit | LIBOR [Member] | Maximum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   1.55%      
Line of Credit | Base Rate [Member] | Minimum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   0.00%      
Line of Credit | Base Rate [Member] | Maximum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   0.55%      
Line of Credit | Federal Funds Effective Swap Rate [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   0.50%      
2015 Term Loan [Member] | Interest Rate Swap [Member]          
Line of Credit Facility [Line Items]          
Derivative, notional amount         $ 150,000,000
Derivative, fixed interest rate (percent)         2.72%
2018 Term Loan [Member]          
Line of Credit Facility [Line Items]          
Debt instrument, face amount       $ 250,000,000  
2018 Term Loan A [Member] | Interest Rate Swap [Member]          
Line of Credit Facility [Line Items]          
Derivative, notional amount       $ 150,000,000  
Derivative, fixed interest rate (percent)       2.31%  
2018 Term Loan A [Member] | LIBOR [Member] | Minimum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   0.85%      
2018 Term Loan A [Member] | LIBOR [Member] | Maximum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   1.75%      
2018 Term Loan A [Member] | Base Rate [Member] | Minimum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   0.00%      
2018 Term Loan A [Member] | Base Rate [Member] | Maximum [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   0.75%      
2018 Term Loan B [Member]          
Line of Credit Facility [Line Items]          
Derivative, notional amount       $ 100,000,000  
2018 Term Loan B [Member] | Interest Rate Swap [Member]          
Line of Credit Facility [Line Items]          
Derivative, notional amount       $ 100,000,000  
Derivative, fixed interest rate (percent)       3.71%  
Credit facility 2018 [Member]          
Line of Credit Facility [Line Items]          
Committed capacity $ 1,500,000,000.0 $ 1,500,000,000.0      
Credit facility 2018 [Member] | Line of Credit          
Line of Credit Facility [Line Items]          
Committed capacity $ 700,000,000.0 $ 700,000,000.0      
Debt instrument, term   4 years      
Debt instrument, maturity date   Mar. 29, 2022      
Number of extensions allowed | extension_option 2        
Term of extension   6 months      
Credit facility 2018 [Member] | 2015 Term Loan [Member]          
Line of Credit Facility [Line Items]          
Debt instrument, face amount $ 150,000,000 $ 150,000,000      
Credit facility 2018 [Member] | 2018 Term Loan [Member]          
Line of Credit Facility [Line Items]          
Debt instrument, face amount 250,000,000 250,000,000      
Credit facility 2018 [Member] | 2018 Term Loan A [Member]          
Line of Credit Facility [Line Items]          
Debt instrument, face amount $ 150,000,000 $ 150,000,000      
Credit facility 2018 [Member] | 2018 Term Loan A [Member] | LIBOR [Member]          
Line of Credit Facility [Line Items]          
Basis spread on variable rate (percent)   1.10%      
Credit facility 2018 [Member] | 2018 Term Loan B [Member]          
Line of Credit Facility [Line Items]          
Proceeds from term loan   $ 100,000,000      
Credit facility 2015 [Member] | Line of Credit          
Line of Credit Facility [Line Items]          
Committed capacity     $ 600,000,000    
Debt instrument, maturity date     Jun. 22, 2019