Fair Value Measurements - Summary of Carrying Amount and Fair Values of Financial Instruments Reported on the Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance sheet assets
Securities available for sale	$ 641,382	$ 460,797
Securities held to maturity	73,749	80,463
State tax credits held for sale	400
Carrying Amount
Balance sheet assets
Cash and due from banks	91,084	54,288
Federal funds sold	1,223	446
Interest-bearing deposits	63,661	145,048
Securities available for sale	641,382	460,797
Securities held to maturity	73,749	80,463
Other investments, at cost	26,661	14,840
Loans held for sale	3,155	9,562
Derivative financial instruments	3,589	4,016
Portfolio loans, net	4,054,473	3,114,752
State tax credits held for sale	43,468	38,071
Accrued interest receivable	14,069	11,117
Balance sheet liabilities
Deposits	4,156,414	3,233,361
Subordinated debentures and notes	118,105	105,540
Federal Home Loan Bank advances	172,743	0
Other borrowings	253,674	276,980
Derivative financial instruments	3,589	4,016
Accrued interest payable	1,730	1,105
Estimated fair value
Balance sheet assets
Cash and due from banks	91,084	54,288
Federal funds sold	1,223	446
Interest-bearing deposits	63,661	145,048
Securities available for sale	641,382	460,797
Securities held to maturity	73,458	79,639
Other investments, at cost	26,661	14,840
Loans held for sale	3,155	9,562
Derivative financial instruments	3,589	4,016
Portfolio loans, net	4,096,741	3,125,701
State tax credits held for sale	44,271	41,264
Accrued interest receivable	14,069	11,117
Balance sheet liabilities
Deposits	4,153,323	3,232,414
Subordinated debentures and notes	105,031	86,052
Federal Home Loan Bank advances	172,893	0
Other borrowings	253,530	276,905
Derivative financial instruments	3,589	4,016
Accrued interest payable	$ 1,730	$ 1,105