Quarterly report pursuant to Section 13 or 15(d)

Unsecured Lines of Credit Payable - Narrative (Details)

v3.7.0.1
Unsecured Lines of Credit Payable - Narrative (Details)
6 Months Ended
Jun. 30, 2017
USD ($)
Sep. 30, 2015
USD ($)
Line of Credit    
Line of Credit Facility [Line Items]    
Line of Credit Facility, Commitment Fee Percentage 0.20%  
Line of Credit Facility, Interest Rate During Period 1.00%  
Revolving Credit Facility    
Line of Credit Facility [Line Items]    
Committed capacity $ 1,000,000,000.0  
Revolving Credit Facility | 2015 Term Loan [Member]    
Line of Credit Facility [Line Items]    
Long-term Line of Credit, Noncurrent   $ 150,000,000
Debt Instrument, Term 5 years 6 months  
Revolving Credit Facility | Line of Credit    
Line of Credit Facility [Line Items]    
Committed capacity $ 600,000,000  
Debt Instrument, Maturity Date Jun. 22, 2019  
line of credit facility, number of extensions allowed 2  
Line of Credit Facility, extension period 6 months  
Minimum [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Line of Credit Facility, Commitment Fee Percentage 0.125%  
Maximum [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Line of Credit Facility, Commitment Fee Percentage 0.30%  
London Interbank Offered Rate (LIBOR) [Member] | 2015 Term Loan [Member]    
Line of Credit Facility [Line Items]    
Debt Instrument, Description of Variable Rate Basis P1M  
London Interbank Offered Rate (LIBOR) [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Debt Instrument, Basis Spread on Variable Rate 1.00%  
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility | 2015 Term Loan [Member]    
Line of Credit Facility [Line Items]    
Debt Instrument, Basis Spread on Variable Rate 1.10%  
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Debt Instrument, Basis Spread on Variable Rate 0.875%  
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Debt Instrument, Basis Spread on Variable Rate 1.55%  
Base Rate [Member] | Minimum [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Debt Instrument, Basis Spread on Variable Rate 0.00%  
Base Rate [Member] | Maximum [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Debt Instrument, Basis Spread on Variable Rate 0.55%  
Federal Funds Effective Swap Rate [Member] | Line of Credit    
Line of Credit Facility [Line Items]    
Debt Instrument, Basis Spread on Variable Rate 0.50%  
Interest Rate Swap [Member] | 2015 Term Loan [Member]    
Line of Credit Facility [Line Items]    
Derivative, Number of Instruments Held 2