Fair Value Disclosure of Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Fixed Rate Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, fair value	$ 2,760.0	$ 2,710.0
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	2,570.0	2,610.0
Variable Rate Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, fair value	910.0	817.7
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	$ 920.0	$ 815.0
Minimum [Member] | Conventional Variable Rate Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Renewal Period	30 days
Maximum [Member] | Conventional Variable Rate Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Renewal Period	90 days