Fair Value of Financial Instruments - Hierarchy Table - Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial assets
Investment securities available-for-sale, at fair value	$ 1,256,655	$ 1,103,222
U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	64,190	60,912
Agency
Financial assets
Investment securities available-for-sale, at fair value	261,558	130,070
Corporate
Financial assets
Investment securities available-for-sale, at fair value	127,802	103,543
Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	294,099	238,630
Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	10,642	24,338
Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	498,364	545,729
Level 1
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	0	0
Financial liabilities
Derivative liabilities	0	0
Level 2
Financial assets
Investment securities available-for-sale, at fair value	1,256,655	1,103,222
Derivative assets	2,853	1,681
Financial liabilities
Derivative liabilities	2,853	1,681
Level 3
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	0	0
Financial liabilities
Derivative liabilities	0	0
Recurring
Financial assets
Investment securities available-for-sale, at fair value	1,256,655	1,103,222
Derivative assets	2,853	1,681
Financial liabilities
Derivative liabilities	2,853	1,681
Recurring | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	64,190	60,912
Recurring | Agency
Financial assets
Investment securities available-for-sale, at fair value	261,558	130,070
Recurring | Corporate
Financial assets
Investment securities available-for-sale, at fair value	127,802	103,543
Recurring | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	294,099	238,630
Recurring | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	10,642	24,338
Recurring | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	498,364	545,729
Recurring | Level 1
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	0	0
Financial liabilities
Derivative liabilities	0	0
Recurring | Level 1 | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Agency
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 2
Financial assets
Investment securities available-for-sale, at fair value	1,256,655	1,103,222
Derivative assets	2,853	1,681
Financial liabilities
Derivative liabilities	2,853	1,681
Recurring | Level 2 | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	64,190	60,912
Recurring | Level 2 | Agency
Financial assets
Investment securities available-for-sale, at fair value	261,558	130,070
Recurring | Level 2 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	127,802	103,543
Recurring | Level 2 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	294,099	238,630
Recurring | Level 2 | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	10,642	24,338
Recurring | Level 2 | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	498,364	545,729
Recurring | Level 3
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	0	0
Financial liabilities
Derivative liabilities	0	0
Recurring | Level 3 | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Agency
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Collateralized mortgage obligation: residential
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Mortgage-backed securities: residential
Financial assets
Investment securities available-for-sale, at fair value	$ 0	$ 0