Fair Value Measurements - Segregated by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Fair Value		$ 603,360
Portfolio loans, net	6,633,501	5,517,780
Mortgage servicing rights	2,200,000
Financial liabilities:
Short-term borrowings	8,551
Junior subordinated debt owed to unconsolidated trusts	71,308	71,155
Level 1 | Carrying Amount
Financial assets:
Cash and cash equivalents	529,288	239,973
Level 1 | Fair Value
Financial assets:
Cash and cash equivalents	529,288	239,973
Level 2 | Carrying Amount
Financial assets:
Fair Value		608,660
Accrued interest receivable	27,109	22,314
Financial liabilities:
Time deposits	1,534,850	1,497,003
Securities sold under agreements to repurchase	205,491	185,796
Short-term borrowings	8,551
Long-term debt	83,600	50,000
Junior subordinated debt owed to unconsolidated trusts	71,308	71,155
Accrued interest payable	5,000	6,568
Level 2 | Fair Value
Financial assets:
Fair Value		603,360
Accrued interest receivable	27,109	22,314
Financial liabilities:
Time deposits	1,538,597	1,482,301
Securities sold under agreements to repurchase	205,491	185,796
Short-term borrowings	8,552
Long-term debt	83,614	49,873
Junior subordinated debt owed to unconsolidated trusts	74,153	65,182
Accrued interest payable	5,000	6,568
Level 3 | Carrying Amount
Financial assets:
Portfolio loans, net	6,633,501	5,517,780
Mortgage servicing rights	12,326	3,315
Other servicing rights	1,071	781
Level 3 | Fair Value
Financial assets:
Portfolio loans, net	6,648,560	5,473,063
Mortgage servicing rights	18,193	11,051
Other servicing rights	1,740	1,443
Level 3 | Senior notes | Carrying Amount
Financial liabilities:
Long-term debt	39,674	39,539
Level 3 | Senior notes | Fair Value
Financial liabilities:
Long-term debt	40,099	39,452
Level 3 | Subordinated debt | Carrying Amount
Financial liabilities:
Long-term debt	59,248	59,147
Level 3 | Subordinated debt | Fair Value
Financial liabilities:
Long-term debt	$ 61,514	$ 58,186