Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Liabilities:
Accrued Interest Payable Fair Value Disclosure	$ 33,810	$ 31,374
Equity investments without readily determinable fair values	27,000	26,400
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value
Financial Assets:
Cash and cash equivalents	698,567	459,606
Financial Liabilities:
Convertible Debt, Fair Value Disclosures	206,210
Quoted Prices in Active Markets for Identical Assets (Level 1) | Reported Value Measurement [Member]
Financial Assets:
Cash and cash equivalents	698,567	459,606
Financial Liabilities:
Convertible Debt, Fair Value Disclosures	199,458
Significant Other Observable Inputs (Level 2) | Estimate of Fair Value
Financial Assets:
Loans held for sale	56,011	25,943
Customers' liabilities on acceptances	1,117	2,281
Financial Liabilities:
Noninterest-bearing deposits	3,108,687	3,022,633
Saving and other interest bearing demand deposits	4,259,707	3,262,399
Time deposits	5,182,405	5,889,030
FHLB advances	628,903	810,812
Federal Funds Purchased, Fair Value Disclosure		180,525
Accrued Interest Payable Fair Value Disclosure	33,810	31,374
Subordinated debentures	114,690	116,542
Bank's liabilities on acceptances outstanding	1,117	2,281
Equity investments without readily determinable fair values	26,967	26,430
Significant Other Observable Inputs (Level 2) | Reported Value Measurement [Member]
Financial Assets:
Loans held for sale	54,271	25,128
Customers' liabilities on acceptances	1,117	2,281
Financial Liabilities:
Noninterest-bearing deposits	3,108,687	3,022,633
Saving and other interest bearing demand deposits	4,259,707	3,262,399
Time deposits	5,158,970	5,870,624
FHLB advances	625,000	821,280
Federal Funds Purchased, Fair Value Disclosure		194,543
Subordinated debentures	103,035	101,929
Bank's liabilities on acceptances outstanding	1,117	2,281
Equity investments without readily determinable fair values	26,967	26,430
Significant Unobservable Inputs (Level 3) | Estimate of Fair Value
Financial Assets:
Loans receivable - net	12,143,727	11,913,906
Servicing Assets, Fair Value Disclosure	18,966	24,762
Significant Unobservable Inputs (Level 3) | Reported Value Measurement [Member]
Financial Assets:
Loans receivable - net	12,181,863	12,005,558
Servicing Assets, Fair Value Disclosure	16,417	23,132
Fair Value Inputs, Level 2 And Level 3 [Member] | Estimate of Fair Value
Financial Assets:
Other Investments, Fair Value Disclosure	29,235	29,374
Accrued Interest Receivable Fair Value Disclosure	30,772	32,225
Fair Value Inputs, Level 2 And Level 3 [Member] | Reported Value Measurement [Member]
Financial Assets:
Other Investments, Fair Value Disclosure	29,162	29,409
Accrued Interest Receivable Fair Value Disclosure	$ 30,772	$ 32,225