Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for loan losses:
Beginning balance	$ 151,859	$ 120,856
Loans charged-off	(22,215)	(8,063)
Charged-off loans recovered	6,306	7,405
Net (charge-offs) recoveries	(15,909)	(658)
Provision for loan losses	25,809	31,661	$ 8,531
Ending balance	161,759	151,859	120,856
Commercial and Industrial
Allowance for loan losses:
Beginning balance	90,956	57,232
Loans charged-off	(13,260)	(2,515)
Charged-off loans recovered	2,397	4,623
Net (charge-offs) recoveries	(10,863)	2,108
Provision for loan losses	23,966	31,616
Ending balance	104,059	90,956	57,232
Commercial Real Estate
Allowance for loan losses:
Beginning balance	49,650	54,954
Loans charged-off	(158)	(348)
Charged-off loans recovered	1,237	417
Net (charge-offs) recoveries	1,079	69
Provision for loan losses	(5,056)	(5,373)
Ending balance	45,673	49,650	54,954
Residential Mortgage
Allowance for loan losses:
Beginning balance	5,041	3,605
Loans charged-off	(126)	(223)
Charged-off loans recovered	66	272
Net (charge-offs) recoveries	(60)	49
Provision for loan losses	79	1,387
Ending balance	5,060	5,041	3,605
Consumer
Allowance for loan losses:
Beginning balance	6,212	5,065
Loans charged-off	(8,671)	(4,977)
Charged-off loans recovered	2,606	2,093
Net (charge-offs) recoveries	(6,065)	(2,884)
Provision for loan losses	6,820	4,031
Ending balance	$ 6,967	$ 6,212	$ 5,065