Accumulated Other Comprehensive Income - Summary of Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 2,851	$ 33,333	$ (4,695)	$ 22,260
Other comprehensive income before reclassifications	3,610	13,293	11,549	25,077
Amounts reclassified from accumulated other comprehensive income	29	0	(364)	(711)
Net other comprehensive income	3,639	13,293	11,185	24,366
Ending balance	6,490	46,626	6,490	46,626
Unrealized holding gains (losses) on AFS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(6,140)	20,301	(14,916)	9,993
Other comprehensive income before reclassifications	5,662	12,712	14,831	23,731
Amounts reclassified from accumulated other comprehensive income	29	0	(364)	(711)
Net other comprehensive income	5,691	12,712	14,467	23,020
Ending balance	(449)	33,013	(449)	33,013
Financial Liability Instruments, Fair Value Option [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	8,727	12,792	9,956	12,033
Other comprehensive income before reclassifications	(2,089)	575	(3,318)	1,334
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Net other comprehensive income	(2,089)	575	(3,318)	1,334
Ending balance	6,638	13,367	6,638	13,367
Impairment loss on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	144	144	144	144
Other comprehensive income before reclassifications	0	0		0
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Net other comprehensive income	0	0	0	0
Ending balance	144	144	144	144
Supplemental Employee Retirement Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	120	96	121	90
Other comprehensive income before reclassifications	37	6	36	12
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Net other comprehensive income	37	6	36	12
Ending balance	$ 157	$ 102	$ 157	$ 102