Derivatives - Additional Information (Detail) $ in Thousands		1 Months Ended		3 Months Ended		9 Months Ended
	Sep. 11, 2015 USD ($) agreement	Aug. 31, 2014 USD ($) agreement	Jan. 31, 2014 USD ($) agreement	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Derivative [Line Items]
Debt Instrument, Term	7 years
Unsecured Term Loan, face amount	$ 260,000
Swaps, notional amount	$ 260,000
Mark-to-Market and Settlement Loss on Interest Rate Protection Agreements				$ 0	$ 0	$ (11,546)	$ 0
Group I Swaps
Derivative [Line Items]
Debt Instrument, Term			7 years
Unsecured Term Loan, face amount			$ 200,000
Swaps, number of instruments held | agreement			4
Swaps, notional amount			$ 200,000
Swaps, variable rate			one month LIBOR
Swaps, weighted average fixed rate			2.29%
Group II Swaps
Derivative [Line Items]
Swaps, number of instruments held | agreement	6
Swaps, notional amount	$ 260,000
Swaps, variable rate	one month LIBOR
Swaps, weighted average fixed rate	1.79%
Group III Swaps
Derivative [Line Items]
Swaps, number of instruments held | agreement		3
Swaps, notional amount		$ 220,000
Swaps, variable rate		three month LIBOR
Swaps, weighted average fixed rate		2.5795%
Reclassification of fair value of interest rate protection agreements						12,990
Settlement payment on Swaps						11,546
Mark-to-Market and Settlement Loss on Interest Rate Protection Agreements						$ 11,546