Loans and Allowance for Credit Losses - Schedule of Activity in Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable Impaired [Line Items]
Balance at beginning of period	$ 43,831	$ 51,139	$ 43,710	$ 54,003
(Charge-offs)/recoveries	32	749	(139)	577
(Payments)/disbursements	(4,547)	(6,423)	(24,300)	(12,346)
Additions	1,087	1,954	21,132	5,185
Balance at end of period	40,403	47,419	40,403	47,419
Commercial Loan [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	18,872	9,043	10,275	12,088
(Charge-offs)/recoveries	12	(7)	(89)	(158)
(Payments)/disbursements	(2,303)	453	(3,307)	(3,525)
Additions	530	1,954	10,232	3,038
Balance at end of period	17,111	11,443	17,111	11,443
Commercial Real Estate [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	19,363	34,927	27,671	34,705
(Charge-offs)/recoveries	13	753	(58)	731
(Payments)/disbursements	(1,057)	(6,601)	(19,321)	(7,570)
Additions			10,027	1,213
Balance at end of period	18,319	29,079	18,319	29,079
Residential [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	3,080	3,771	3,390	3,315
(Charge-offs)/recoveries				23
(Payments)/disbursements	(865)	(75)	(1,175)	(144)
Additions	557		557	502
Balance at end of period	2,772	3,696	2,772	3,696
Consumer Loan [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	2,516	3,398	2,374	3,895
(Charge-offs)/recoveries	7	3	8	(19)
(Payments)/disbursements	(322)	(200)	(497)	(1,107)
Additions			316	432
Balance at end of period	$ 2,201	$ 3,201	$ 2,201	$ 3,201