Fair Value Measurements - Carrying Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial Assets:
Equity security	$ 114	$ 146
Carrying Value
Financial Assets:
Cash and cash equivalents	161,910	103,015
Investment securities available for sale	976,095	810,530
Federal Home Loan Bank stock	6,076	8,347
Loans held for sale	1,555	2,288
Total loans receivable, net	3,619,118	2,816,985
Accrued interest receivable	15,403	12,244
Derivative assets - interest rate swaps	5,095	3,418
Equity security	114
Financial Liabilities:
Noninterest deposits, interest bearing demand deposits, money market accounts and savings accounts	3,965,510	2,994,662
Certificate of deposit accounts	466,892	398,398
Federal Home Loan Bank advances		92,500
Securities sold under agreement to repurchase	31,487	31,821
Junior subordinated debentures	20,302	20,009
Accrued interest payable	191	162
Derivative liabilities - interest rate swaps	5,095	3,418
Fair Value
Financial Assets:
Cash and cash equivalents	161,910	103,015
Investment securities available for sale	976,095	810,530
Loans held for sale	1,605	2,364
Total loans receivable, net	3,614,348	2,810,401
Accrued interest receivable	15,403	12,244
Derivative assets - interest rate swaps	5,095	3,418
Equity security	0
Financial Liabilities:
Noninterest deposits, interest bearing demand deposits, money market accounts and savings accounts	3,965,510	2,994,662
Certificate of deposit accounts	470,222	397,039
Federal Home Loan Bank advances		92,500
Securities sold under agreement to repurchase	31,487	31,821
Junior subordinated debentures	20,500	18,500
Accrued interest payable	191	162
Derivative liabilities - interest rate swaps	5,095	3,418
Fair Value | Level 1
Financial Assets:
Cash and cash equivalents	161,910	103,015
Investment securities available for sale	15,936	146
Loans held for sale	0	0
Total loans receivable, net	0	0
Accrued interest receivable	68	23
Derivative assets - interest rate swaps	0	0
Equity security	114
Financial Liabilities:
Noninterest deposits, interest bearing demand deposits, money market accounts and savings accounts	3,965,510	2,994,662
Certificate of deposit accounts	0	0
Federal Home Loan Bank advances		0
Securities sold under agreement to repurchase	31,487	31,821
Junior subordinated debentures	0	0
Accrued interest payable	63	45
Derivative liabilities - interest rate swaps	0	0
Fair Value | Level 2
Financial Assets:
Cash and cash equivalents	0	0
Investment securities available for sale	960,159	810,384
Loans held for sale	1,605	2,364
Total loans receivable, net	0	0
Accrued interest receivable	4,091	3,772
Derivative assets - interest rate swaps	5,095	3,418
Equity security	0
Financial Liabilities:
Noninterest deposits, interest bearing demand deposits, money market accounts and savings accounts	0	0
Certificate of deposit accounts	470,222	397,039
Federal Home Loan Bank advances		92,500
Securities sold under agreement to repurchase	0	0
Junior subordinated debentures	0	0
Accrued interest payable	81	79
Derivative liabilities - interest rate swaps	5,095	3,418
Fair Value | Level 3
Financial Assets:
Cash and cash equivalents	0	0
Investment securities available for sale	0	0
Loans held for sale	0	0
Total loans receivable, net	3,614,348	2,810,401
Accrued interest receivable	11,244	8,449
Derivative assets - interest rate swaps	0	0
Equity security	0
Financial Liabilities:
Noninterest deposits, interest bearing demand deposits, money market accounts and savings accounts	0	0
Certificate of deposit accounts	0	0
Federal Home Loan Bank advances		0
Securities sold under agreement to repurchase	0	0
Junior subordinated debentures	20,500	18,500
Accrued interest payable	47	38
Derivative liabilities - interest rate swaps	$ 0	$ 0