Allowance for Credit Losses - Collateral Dependent Loans by Class of Loan (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	$ 7,183,168	$ 7,225,860
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	92,464	108,525
Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	11,980	16,699
Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	5,350	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	5,676,683	5,673,707
Commercial | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	2,780,327	2,791,947
Commercial | Commercial real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	86,683	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	5,350	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	1,699,588	1,559,552
Commercial | Commercial and industrial | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	335	1,040
Commercial | Commercial and industrial | Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	11,968	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	449,459	466,077
Commercial | Commercial construction | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	3,245	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	1,069,078	1,160,067
Commercial | Business banking | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,856	3,085
Commercial | Business banking | Business Assets
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	12	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	1,506,485	1,552,153
Consumer | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	321,800	303,900
Consumer | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,104,099	1,167,332
Consumer | Consumer real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	345	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