Fair Value of Financial Instruments - Hierarchy Table - Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financial assets
Investment securities available-for-sale, at fair value	$ 1,337,761	$ 1,368,384
U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	32,833	63,555
Agency
Financial assets
Investment securities available-for-sale, at fair value	247,766	246,358
Corporate
Financial assets
Investment securities available-for-sale, at fair value	176,033	151,353
Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	407,097	397,298
Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	9,656	9,984
Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	464,376	499,836
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	1,337,761	1,368,384
Derivative assets	10,961	2,103
Financial liabilities
Derivative liabilities	11,013	2,103
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	1,337,761	1,368,384
Derivative assets	10,961	2,103
Financial liabilities
Derivative liabilities	11,013	2,103
Recurring | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	32,833	63,555
Recurring | Agency
Financial assets
Investment securities available-for-sale, at fair value	247,766	246,358
Recurring | Corporate
Financial assets
Investment securities available-for-sale, at fair value	176,033	151,353
Recurring | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	407,097	397,298
Recurring | Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	9,656	9,984
Recurring | Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	464,376	499,836
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 obligations
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Mortgage-backed securities
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	1,337,761	1,368,384
Derivative assets	10,961	2,103
Financial liabilities
Derivative liabilities	11,013	2,103
Recurring | Level 2 | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	32,833	63,555
Recurring | Level 2 | Agency
Financial assets
Investment securities available-for-sale, at fair value	247,766	246,358
Recurring | Level 2 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	176,033	151,353
Recurring | Level 2 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	407,097	397,298
Recurring | Level 2 | Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	9,656	9,984
Recurring | Level 2 | Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	464,376	499,836
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 obligations
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	$ 0	$ 0