Loans and Loans Held for Sale - Additional Information (Details) $ in Thousands			3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($) relationship loan	Dec. 31, 2020 USD ($)	Jun. 30, 2021 USD ($) relationship loan	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($) loan	Jun. 30, 2021 USD ($) relationship loan	Jun. 30, 2020 USD ($) loan	Dec. 31, 2020 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income	$ 16,500	$ 16,000	$ 16,500			$ 16,500		$ 16,000
Purchase accounting fair value adjustments	6,900	8,600
Total loans	6,897,715	7,108,248	6,897,715			6,897,715		7,108,248
Loans held for investment, outstanding balance	$ 7,007,351	7,225,860	$ 7,007,351			$ 7,007,351		7,225,860
Threshold period of satisfactory performance for troubled debt restructuring to be restored to accruing status						6 months
Number of troubled debt restructuring loans returned to accruing status | loan			4		4	5	4
Financing receivable, troubled debt restructuring, returned to accruing status			$ 500		$ 100	$ 500	$ 100
Number of commitments to lend additional funds on TDRs | loan	14		14			14
Commitments to lend additional funds on TDRs	$ 700		$ 700			$ 700
Minimum period of loan payment defaults following restructure for TDRs to be in default						90 days
Number of defaulted TDRs that were restructured within the last twelve months prior to defaulting | loan			0		1		11
Amount of defaulted TDRs that were restructured within the last twelve months prior to defaulting					$ 100		$ 21,100
Number of commercial real estate relationships | relationship	3		3			3
Restructured loans			$ 1,377		1,303	$ 8,159	7,852
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	$ 5,499,044	$ 5,673,707	$ 5,499,044			$ 5,499,044		$ 5,673,707
Financing receivable, before allowance for credit loss, reclassification during period				$ 90,200
Percentage of commercial loans in total portfolio loans	78.50%	78.50%	78.50%			78.50%		78.50%
Commercial | CARES Act, Paycheck Protection Program Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of modified loans | loan						42		52
Modified loans						$ 68,700		$ 195,600
Business banking portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	$ 1,100,000	$ 1,200,000	$ 1,100,000			1,100,000		1,200,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	1,508,307	1,552,153	1,508,307			1,508,307		1,552,153
Financing receivable, before allowance for credit loss, reclassification during period				$ 23,200
CARES Act, Paycheck Protection Program Loans | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	336,100	465,000	336,100			336,100		465,000
Commercial real estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	2,740,296	2,791,947	2,740,296			2,740,296		2,791,947
Restructured loans			0		0	0	2,210
Commercial real estate | Business banking portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	506,200	453,000	506,200			506,200		453,000
Commercial and industrial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	1,546,247	1,559,552	1,546,247			1,546,247		1,559,552
Restructured loans			0		75	6,229	2,143
Commercial and industrial | Business banking portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	228,100	394,900	228,100			228,100		394,900
Commercial construction | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	467,871	466,077	467,871			467,871		466,077
Restructured loans			0		701	0	2,572
Commercial construction | Business banking portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	10,300	8,200	10,300			10,300		8,200
Consumer real estate | Business banking portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	326,200		326,200			326,200
Consumer real estate | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	1,093,878	1,167,332	1,093,878			1,093,878		1,167,332
Restructured loans			247		500	720	900
Other consumer | Business banking portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	30		30			30
Other consumer | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	88,184	80,885	88,184			88,184		80,885
Restructured loans			0		0	0	0
Business banking | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	1,070,875	1,160,067	1,070,875			1,070,875		1,160,067
Restructured loans			1,130		$ 27	1,210	$ 27
Business banking | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance		303,900						303,900
CRE and commercial construction | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, outstanding balance	$ 3,700,000	$ 3,700,000	$ 3,700,000			$ 3,700,000		$ 3,700,000
Combined percentage of commercial real estate and commercial construction in total commercial loans	67.70%	65.60%	67.70%			67.70%		65.60%
Combined percentage of commercial real estate and commercial construction in total portfolio loans	53.20%	51.50%	53.20%			53.20%		51.50%
Out of market exposure of combined portfolio (percent)	5.40%	5.90%	5.40%			5.40%		5.90%
Percentage of total loans out-of-state excluding contiguous states	2.90%	3.00%	2.90%			2.90%		3.00%
Nonperforming TDRs
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, nonperforming assets, period increase (decrease)						$ 34,200
Nonperforming TDRs | Commercial real estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured loans						14,400
Amount charged down						4,900
Nonperforming TDRs | Commercial and industrial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amount charged down						$ 3,900