Derivatives and Hedging Fair Value of Derivative Contracts (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Notional Amount		$ 993,485	$ 800,478	$ 647,703
Derivative Asset, Fair Value		4,220	3,569	7
Derivative Liability, Fair Value		65,749	64,785	57,820
Notional Amount, Netting Adjustments	[1]	0	0	0
Derivative Netting Adjustments	[1]	1,869	0	0
Positive NPVs		2,351	3,569	7
Negative NPVs		63,880	64,785	57,820
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Notional Amount		993,485	800,478	647,703
Derivative Asset, Fair Value		4,220	3,569	7
Derivative Liability, Fair Value		$ 65,749	$ 64,785	$ 57,820

[1] Netting adjustments represent the amounts recorded to convert the Company's derivative balances from a gross basis to a net basis in accordance with the applicable accounting guidance.