Summary of Company's Interest Rate Derivatives (Detail) - Derivatives not designated as hedging instruments - USD ($)		Jun. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Notional Amount		$ 800,000,000	$ 800,000,000
Fair Value		(43,200,000)	(28,400,000)
Interest Rate Swap L
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	75,000,000	75,000,000
Fair Value	[1]	(5,000,000)	(3,600,000)
Interest Rate Swap M
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	100,000,000	100,000,000
Fair Value	[1]	(6,700,000)	(4,800,000)
Interest Rate Swap N
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	75,000,000	75,000,000
Fair Value	[1]	(4,900,000)	(3,500,000)
Interest Rate Swap O
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	75,000,000	75,000,000
Fair Value	[1]	(4,500,000)	(3,100,000)
Interest Rate Swap P
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	75,000,000	75,000,000
Fair Value	[1]	(4,200,000)	(2,800,000)
Interest Rate Swap Q
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	50,000,000	50,000,000
Fair Value	[1]	(2,700,000)	(1,700,000)
Interest Rate Swap R
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	50,000,000	50,000,000
Fair Value	[1]	(2,700,000)	(1,700,000)
Interest Rate Swap S
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	50,000,000	50,000,000
Fair Value	[1]	(2,300,000)	(1,400,000)
Interest Rate Swap T
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	75,000,000	75,000,000
Fair Value	[1]	(3,500,000)	(2,100,000)
Interest Rate Swap U
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	50,000,000	50,000,000
Fair Value	[1]	(2,200,000)	(1,200,000)
Interest Rate Swap V
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	50,000,000	50,000,000
Fair Value	[1]	(2,000,000)	(1,200,000)
Interest Rate Swap W
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	25,000,000	25,000,000
Fair Value	[1]	(900,000)	(500,000)
Interest Rate Swap X
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	50,000,000	50,000,000
Fair Value	[1]	$ (1,600,000)	$ (800,000)

[1] includes LIBOR floor of 1.00%