Loans Held for Sale, Loans and Allowance for Credit Losses - Total Loans Outstanding by Portfolio Segment and Class of Financing Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	$ 13,392,191	$ 12,983,655	$ 13,710,243
Commercial and Industrial
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	7,749,310	7,438,658	7,481,688
Commercial and Industrial | General C&I
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	4,694,114	4,517,016
Commercial and Industrial | Energy Sector
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	1,480,497	1,419,957
Commercial and Industrial | Restaurant Industry
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	1,082,602	1,027,421
Commercial and Industrial | Healthcare
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	492,097	474,264
Commercial Real Estate
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	2,980,760	2,887,272	2,830,195
Commercial Real Estate | Industrial, Retail, and Other
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	1,754,881	1,691,694
Commercial Real Estate | Multifamily
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	692,168	659,902
Commercial Real Estate | Office
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	533,711	535,676
Consumer
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	2,662,121	2,657,725	$ 2,639,518
Consumer | Residential
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	2,576,073	2,568,295
Consumer | Other
Accounts Notes And Loans Receivable [Line Items]
Total loan outstanding and financing receivable	$ 86,048	$ 89,430