Loans and Allowance for Credit Losses - Schedule of Activity in Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable Impaired [Line Items]
Balance at beginning of period	$ 46,343	$ 53,484	$ 43,710	$ 54,003
(Charge-offs)/recoveries	(85)	(354)	(172)	(172)
(Payments)/disbursements	(16,961)	(3,685)	(19,751)	(5,923)
Additions	14,534	1,694	20,044	3,231
Balance at end of period	43,831	51,139	43,831	51,139
Commercial Loan [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	11,646	11,918	10,275	12,088
(Charge-offs)/recoveries	(93)	(22)	(100)	(151)
(Payments)/disbursements	25	(3,398)	(1,004)	(3,978)
Additions	7,294	545	9,701	1,084
Balance at end of period	18,872	9,043	18,872	9,043
Commercial Real Estate [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	29,137	34,488	27,671	34,705
(Charge-offs)/recoveries	4	(12)	(71)	(22)
(Payments)/disbursements	(16,702)	(196)	(18,264)	(969)
Additions	6,924	647	10,027	1,213
Balance at end of period	19,363	34,927	19,363	34,927
Residential [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	3,247	3,058	3,390	3,315
(Charge-offs)/recoveries				23
(Payments)/disbursements	(167)	211	(310)	(69)
Additions		502		502
Balance at end of period	3,080	3,771	3,080	3,771
Consumer Loan [Member]
Financing Receivable Impaired [Line Items]
Balance at beginning of period	2,313	4,020	2,374	3,895
(Charge-offs)/recoveries	4	(320)	(1)	(22)
(Payments)/disbursements	(117)	(302)	(173)	(907)
Additions	316		316	432
Balance at end of period	$ 2,516	$ 3,398	$ 2,516	$ 3,398