Commitments and Contingencies - Gains (Losses) Related to Interest Rate Derivatives Designated as Hedges of Fair Value (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) included in the consolidated statements of income	$ (792)	$ (744)	$ 690
Fair value hedge | Interest rate swaps | Interest income
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) included in the consolidated statements of income	290	348	320
Fair value hedge | Interest rate swaps | Interest expense
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) included in the consolidated statements of income	0	0	6,670
Fair value hedge | Interest rate caps and swaps | Derivatives designated as hedging instruments | Interest income
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) included in the consolidated statements of income	(290)	(348)	(320)
Fair value hedge | Interest rate caps and swaps | Derivatives designated as hedging instruments | Interest expense
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) included in the consolidated statements of income	$ 0	$ 0	$ (6,645)