Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments Not Recorded at Fair Value on Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Estimated fair value | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	$ 63,031	$ 63,934
Estimated fair value | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	5,049,215	4,253,239
Estimated fair value | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	39,037	39,169
Estimated fair value | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	5,536,456	4,583,047
Estimated fair value | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	132,301	106,316
Estimated fair value | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	389,471	70,000
Estimated fair value | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	197,988	223,260
Level 1 | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 1 | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	4,736,768	3,903,556
Level 1 | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 1 | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 2 | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	63,031	63,934
Level 2 | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 2 | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 2 | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 2 | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	132,301	106,316
Level 2 | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	389,471	70,000
Level 2 | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	197,988	223,260
Level 3 | Securities held to maturity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	0	0
Level 3 | Portfolio loans, net
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	5,049,215	4,253,239
Level 3 | State tax credits, held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial assets not on condensed consolidated balance sheets at fair value	39,037	39,169
Level 3 | Deposits
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	799,688	679,491
Level 3 | Subordinated debentures and notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 3 | Federal Home Loan Bank advances
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	0	0
Level 3 | Other Borrowings
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial liabilities not on condensed consolidated balance sheets at fair value	$ 0	$ 0