Allowance for Credit Losses - Collateral Dependent Loans by Class of Loan (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	$ 7,007,351	$ 7,225,860
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	81,767	108,525
Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	15,602	16,699
Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	689
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	5,499,044	5,673,707
Commercial | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	2,740,296	2,791,947
Commercial | Commercial real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	76,437	100,450
Commercial | Commercial real estate | Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Commercial real estate | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Commercial real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,546,247	1,559,552
Commercial | Commercial and industrial | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	302	1,040
Commercial | Commercial and industrial | Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	14,461	15,080
Commercial | Commercial and industrial | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Commercial and industrial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	467,871	466,077
Commercial | Commercial construction | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	3,222	3,552
Commercial | Commercial construction | Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Commercial construction | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Commercial construction | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,070,875	1,160,067
Commercial | Business banking | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,806	3,085
Commercial | Business banking | Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,141	1,619
Commercial | Business banking | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Commercial | Business banking | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	689
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,508,307	1,552,153
Consumer | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance		303,900
Consumer | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,093,878	1,167,332
Consumer | Consumer real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	398
Consumer | Consumer real estate | Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Consumer | Consumer real estate | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0	0
Consumer | Consumer real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	$ 0	$ 0