Fair Value of Financial Instruments - Hierarchy Table - Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financial assets
Investment securities available-for-sale, at fair value	$ 874,700	$ 787,429
Agency
Financial assets
Investment securities available-for-sale, at fair value	41,077	47,209
Corporate
Financial assets
Investment securities available-for-sale, at fair value	92,502	79,546
Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	219,901	232,128
Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	29,158	33,781
Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	492,062	394,765
Level 1
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative asset	0	0
Financial liabilities
Derivative liability	0	0
Level 2
Financial assets
Investment securities available-for-sale, at fair value	874,700	787,429
Derivative asset	3,272	1,135
Financial liabilities
Derivative liability	3,272	1,135
Level 3
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative asset	0	0
Financial liabilities
Derivative liability	0	0
Recurring basis
Financial assets
Investment securities available-for-sale, at fair value	874,700	787,429
Derivative asset	3,272	1,135
Financial liabilities
Derivative liability	3,272	1,135
Recurring basis | Agency
Financial assets
Investment securities available-for-sale, at fair value	41,077	47,209
Recurring basis | Corporate
Financial assets
Investment securities available-for-sale, at fair value	92,502	79,546
Recurring basis | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	219,901	232,128
Recurring basis | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	29,158	33,781
Recurring basis | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	492,062	394,765
Recurring basis | Level 1
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative asset	0	0
Financial liabilities
Derivative liability	0	0
Recurring basis | Level 1 | Agency
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 1 | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 2
Financial assets
Investment securities available-for-sale, at fair value	874,700	787,429
Derivative asset	3,272	1,135
Financial liabilities
Derivative liability	3,272	1,135
Recurring basis | Level 2 | Agency
Financial assets
Investment securities available-for-sale, at fair value	41,077	47,209
Recurring basis | Level 2 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	92,502	79,546
Recurring basis | Level 2 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	219,901	232,128
Recurring basis | Level 2 | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	29,158	33,781
Recurring basis | Level 2 | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	492,062	394,765
Recurring basis | Level 3
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative asset	0	0
Financial liabilities
Derivative liability	0	0
Recurring basis | Level 3 | Agency
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring basis | Level 3 | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	$ 0	$ 0