Fair Value Measurements - Summary of Carrying Amount and Fair Values of Financial Instruments Reported on the Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Balance sheet assets
Securities available for sale	$ 1,247,333	$ 721,369
Securities held to maturity	60,786	65,679
State tax credits held for sale	0	0
Carrying Amount
Balance sheet assets
Cash and due from banks	153,730	91,511
Federal funds sold	2,829	1,714
Interest-bearing deposits	103,918	106,512
Securities available for sale	1,247,333	721,369
Securities held to maturity	60,786	65,679
Other investments, at cost	46,867	26,654
Loans held for sale	6,281	392
Derivatives	13,561	3,023
Portfolio loans, net	5,183,459	4,306,525
State tax credits held for sale	43,808	37,587
Accrued interest receivable	21,097	16,069
Balance sheet liabilities
Deposits	5,624,380	4,587,985
Subordinated debentures and notes	141,179	118,156
Federal Home Loan Bank advances	461,426	70,000
Other borrowings and notes payable	199,634	223,450
Derivatives	18,451	3,023
Accrued interest payable	2,907	1,977
Estimated fair value
Balance sheet assets
Cash and due from banks	153,730	91,511
Federal funds sold	2,829	1,714
Interest-bearing deposits	103,918	106,512
Securities available for sale	1,247,333	721,369
Securities held to maturity	61,623	63,934
Other investments, at cost	46,867	26,654
Loans held for sale	6,281	392
Derivatives	13,561	3,023
Portfolio loans, net	5,123,351	4,253,239
State tax credits held for sale	46,981	39,169
Accrued interest receivable	21,097	16,069
Balance sheet liabilities
Deposits	5,604,045	4,583,047
Subordinated debentures and notes	131,603	106,316
Federal Home Loan Bank advances	464,033	70,000
Other borrowings and notes payable	199,539	223,260
Derivatives	18,451	3,023
Accrued interest payable	$ 2,907	$ 1,977