Basis of Presentation - Correction of Prior Period Balances (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Noninterest income - Other income	$ 6,066	$ 4,862	$ 17,312	$ 14,011
Noninterest expense - Other operating expense	$ 10,644	8,811	29,275	$ 24,552
Immaterial error, cash servicing fees
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Noninterest income - Other income		4,862	14,011
Noninterest expense - Other operating expense		8,811	24,552
Immaterial error, cash servicing fees | As originally reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Noninterest income - Other income		4,125	12,017
Noninterest expense - Other operating expense		8,074	22,558
Immaterial error, cash servicing fees | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Noninterest income - Other income		737	1,994
Noninterest expense - Other operating expense		$ 737	$ 1,994