Loans and Allowance for Credit Losses - Schedule of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	$ 54,619	$ 55,461
Charge-offs	(8,445)	(2,892)
Recoveries	1,909	1,947
Provision for Credit Losses	16,950	1,043
Balance at End of Period	106,380	55,559
Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	54,619
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	22,585	21,742
Charge-offs	(5,042)	(160)
Recoveries	357	375
Provision for Credit Losses	7,301	(1,551)
Balance at End of Period	31,125	20,406
Commercial | Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	21,359
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	21,588	23,470
Charge-offs	(1,292)	(235)
Recoveries	669	570
Provision for Credit Losses	8,643	1,364
Balance at End of Period	54,103	25,169
Commercial real estate | Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	20,535
BBCC
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(15)
Recoveries	66
Provision for Credit Losses	(615)
Balance at End of Period	5,417
BBCC | Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	2,279
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	2,299	2,277
Charge-offs	(300)	(178)
Recoveries	169	72
Provision for Credit Losses	483	131
Balance at End of Period	9,637	2,302
Residential real estate | Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	2,299
Home equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(118)
Recoveries	82
Provision for Credit Losses	(8)
Balance at End of Period	1,610
Home equity | Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	965
Indirect
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(1,203)
Recoveries	414
Provision for Credit Losses	805
Balance at End of Period	3,666
Indirect | Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	5,319
Direct
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	(475)
Recoveries	152
Provision for Credit Losses	341
Balance at End of Period	822
Direct | Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	1,863
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	$ 8,147	7,972
Charge-offs		(2,319)
Recoveries		930
Provision for Credit Losses		1,099
Balance at End of Period		$ 7,682