Loans and Allowance for Credit Losses - Schedule of Composition of Loans and Impact of Adoption (Details) - USD ($) $ in Thousands	Dec. 31, 2020		Jan. 01, 2020	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 13,786,479			$ 12,117,524
Allowance	(131,388)	[1]		(54,619)	[1]	$ (55,461)	$ (50,381)
Net loans	13,655,091			12,062,905
Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans			$ 4,478
Allowance			(41,347)	(41,347)
Net loans			(36,869)
Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	13,786,479		12,122,002
Allowance	(131,388)		(95,966)	(95,966)
Net loans	13,655,091		12,026,036
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	3,956,422			2,890,296
Allowance	(30,567)			(21,359)		(21,742)	(19,246)
Commercial | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(198,722)		2,679
Allowance			(7,150)	(7,150)
Commercial | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	3,757,700		2,817,833
Allowance			(28,509)	(28,509)
Commercial | PPP Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	943,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	5,946,512			5,166,792
Allowance	(75,810)			(20,535)		(23,470)	(21,436)
Commercial real estate | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(171,701)		1,637
Allowance			(25,548)	(25,548)
Commercial real estate | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	5,774,811		4,890,890
Allowance			(46,083)	(46,083)
BBCC
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance	(6,120)			(2,279)
BBCC | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	370,423		33
Allowance			(3,702)	(3,702)
BBCC | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	370,423		352,714
Allowance			(5,981)	(5,981)
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,248,422			2,334,289
Allowance	(12,608)			(2,299)		(2,277)	(1,763)
Residential real estate | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	0		105
Allowance			(6,986)	(6,986)
Residential real estate | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,248,422		2,334,394
Allowance			(9,285)	(9,285)
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,635,123			1,726,147
Allowance						$ (7,972)	$ (7,936)
Consumer | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(1,635,123)
Indirect
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	913,902
Allowance	(3,580)			(5,319)
Indirect | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	913,902		10
Allowance			1,669	1,669
Indirect | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	913,902		935,594
Allowance			(3,650)	(3,650)
Direct
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	164,807
Allowance	(855)			(1,863)
Direct | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	164,807		2
Allowance			1,059	1,059
Direct | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	164,807		228,526
Allowance			(804)	(804)
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	556,414
Allowance	(1,848)			(965)
Home equity | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	556,414		12
Allowance			(689)	(689)
Home equity | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	556,414		562,051
Allowance			(1,654)	$ (1,654)
Direct Finance Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 32,300		$ 47,200

[1] Beginning January 1, 2020, calculation is based on current expected loss methodology. Prior to January 1, 2020, calculation was based on incurred loss methodology.