Allowance for Credit Losses - Collateral Dependent Loans by Class of Loan (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	$ 7,225,860		$ 7,137,152
Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	108,525
Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	16,699
Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	689
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	5,977,643		5,756,971
Commercial | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	2,791,947	$ 3,416,518	3,059,592
Commercial | Commercial real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	100,450
Commercial | Commercial real estate | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Commercial real estate | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Commercial real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,559,552	1,720,833	1,480,529
Commercial | Commercial and industrial | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,040
Commercial | Commercial and industrial | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	15,080
Commercial | Commercial and industrial | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Commercial and industrial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Other Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	466,077	375,445	370,060
Commercial | Other Consumer | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	3,552
Commercial | Other Consumer | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Other Consumer | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Other Consumer | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,160,067	0	846,790
Commercial | Business banking | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	3,085
Commercial | Business banking | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,619
Commercial | Business banking | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Commercial | Business banking | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	689
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,248,217		1,380,181
Consumer | Other Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance			8,390
Consumer | Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	1,167,332	$ 1,545,323	$ 1,295,207
Consumer | Consumer real estate | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	398
Consumer | Consumer real estate | Blanket Lien
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Consumer | Consumer real estate | Investment/Cash
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	0
Consumer | Consumer real estate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held for investment, outstanding balance	$ 0