Derivative Instruments - Gross Amounts of Recognized Derivative Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amounts of recognized assets	$ 25,241	$ 120,385
Gross amounts offset on balance sheet	(10,978)	(11,903)
Net amounts of assets on balance sheet	14,263	108,482
Gross amounts of recognized liabilities	(29,057)	(19,192)
Gross amounts offset on balance sheet	10,978	11,903
Net amounts of liabilities on balance sheet	$ (18,079)	$ (7,289)