Fair Value Measurements - Segregated by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial assets:
Portfolio loans, net	$ 7,132,974	$ 6,633,501
Financial liabilities:
Short-term borrowings	24,648	8,551
Junior subordinated debt owed to unconsolidated trusts	71,387	71,308
Level 1 | Carrying Amount
Financial assets:
Cash and cash equivalents	1,050,072	529,288
Level 1 | Fair Value
Financial assets:
Cash and cash equivalents	1,050,072	529,288
Level 2 | Carrying Amount
Financial assets:
Accrued interest receivable	34,035	27,109
Financial liabilities:
Time deposits	1,363,497	1,534,850
Securities sold under agreements to repurchase	194,249	205,491
Short-term borrowings	24,648	8,551
Long-term debt	35,101	83,600
Junior subordinated debt owed to unconsolidated trusts	71,387	71,308
Accrued interest payable	4,659	5,000
Level 2 | Fair Value
Financial assets:
Accrued interest receivable	34,035	27,109
Financial liabilities:
Time deposits	1,381,268	1,538,597
Securities sold under agreements to repurchase	194,249	205,491
Short-term borrowings	24,642	8,552
Long-term debt	35,252	83,614
Junior subordinated debt owed to unconsolidated trusts	58,954	74,153
Accrued interest payable	4,659	5,000
Level 3 | Carrying Amount
Financial assets:
Portfolio loans, net	7,132,974	6,633,501
Mortgage servicing rights	12,085	12,326
Other servicing rights	1,136	1,071
Level 3 | Fair Value
Financial assets:
Portfolio loans, net	7,148,040	6,648,560
Mortgage servicing rights	12,481	18,193
Other servicing rights	1,623	1,740
Level 3 | Senior notes | Carrying Amount
Financial liabilities:
Long-term debt	39,741	39,674
Level 3 | Senior notes | Fair Value
Financial liabilities:
Long-term debt	40,111	40,099
Level 3 | Subordinated debt | Carrying Amount
Financial liabilities:
Long-term debt	181,995	59,248
Level 3 | Subordinated debt | Fair Value
Financial liabilities:
Long-term debt	$ 175,284	$ 61,514