Loans and Allowance for Credit Losses - Schedule of Activity in Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financing Receivable Impaired [Line Items]
Balance at beginning of period	$ 43,710	$ 54,003
(Charge-offs)/recoveries	(85)	182
(Payments)/disbursements	(2,792)	(2,238)
Additions	5,510	1,537
Balance at end of period	46,343	53,484
Commercial Loan [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	10,275	12,088
(Charge-offs)/recoveries	(7)	(129)
(Payments)/disbursements	(1,029)	(580)
Additions	2,407	539
Balance at end of period	11,646	11,918
Commercial Real Estate [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	27,671	34,705
(Charge-offs)/recoveries	(75)	(10)
(Payments)/disbursements	(1,562)	(773)
Additions	3,103	566
Balance at end of period	29,137	34,488
Residential [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	3,390	3,315
(Charge-offs)/recoveries		23
(Payments)/disbursements	(143)	(280)
Balance at end of period	3,247	3,058
Consumer Loan [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	2,374	3,895
(Charge-offs)/recoveries	(3)	298
(Payments)/disbursements	(58)	(605)
Additions		432
Balance at end of period	$ 2,313	$ 4,020