Loans and Allowance for Loan Losses - Schedule of Composition of Loan (Detail) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 12,117,524	$ 12,243,892
Allowance for loan losses	(54,619)	(55,461)	$ (50,381)	$ (49,808)
Net loans	12,062,905	12,188,431
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,890,296	3,232,970
Allowance for loan losses	(22,585)	(21,742)	$ (19,246)	$ (21,481)
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,334,289	2,248,404
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	5,166,792	4,958,851
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,726,147	1,803,667
Consumer [Member] | Consumer Credit - Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	559,021	589,322
Construction [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	713,092	504,625
Other [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	4,453,700	4,454,226
Other [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	149,839	154,712
Consumer Credit - Auto [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 1,017,287	$ 1,059,633