Fair Value of Financial Instruments - Assets measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Level 1
Financial assets
Derivative asset	$ 0	$ 0
Financial liabilities
Derivative liability	0	0
Level 2
Financial assets
Derivative asset	2,103	1,681
Financial liabilities
Derivative liability	2,103	1,681
Level 3
Financial assets
Derivative asset	0	0
Financial liabilities
Derivative liability	0	0
Recurring basis
Financial assets
Total securities available for sale:	1,368,384	1,103,222
Derivative asset	2,103	1,681
Financial liabilities
Derivative liability	2,103	1,681
Recurring basis | Level 1
Financial assets
Total securities available for sale:	0	0
Derivative asset	0	0
Financial liabilities
Derivative liability	0	0
Recurring basis | Level 2
Financial assets
Total securities available for sale:	1,368,384	1,103,222
Derivative asset	2,103	1,681
Financial liabilities
Derivative liability	2,103	1,681
Recurring basis | Level 3
Financial assets
Total securities available for sale:	0	0
Derivative asset	0	0
Financial liabilities
Derivative liability	0	0
Recurring basis | U.S. Treasury
Financial assets
Total securities available for sale:	63,555	60,912
Recurring basis | U.S. Treasury | Level 1
Financial assets
Total securities available for sale:	0	0
Recurring basis | U.S. Treasury | Level 2
Financial assets
Total securities available for sale:	63,555	60,912
Recurring basis | U.S. Treasury | Level 3
Financial assets
Total securities available for sale:	0	0
Recurring basis | Agency
Financial assets
Total securities available for sale:	246,358	130,070
Recurring basis | Agency | Level 1
Financial assets
Total securities available for sale:	0	0
Recurring basis | Agency | Level 2
Financial assets
Total securities available for sale:	246,358	130,070
Recurring basis | Agency | Level 3
Financial assets
Total securities available for sale:	0	0
Recurring basis | Corporate
Financial assets
Total securities available for sale:	151,353	103,543
Recurring basis | Corporate | Level 1
Financial assets
Total securities available for sale:	0	0
Recurring basis | Corporate | Level 2
Financial assets
Total securities available for sale:	151,353	103,543
Recurring basis | Corporate | Level 3
Financial assets
Total securities available for sale:	0	0
Recurring basis | Municipal bonds
Financial assets
Total securities available for sale:	397,298	238,630
Recurring basis | Municipal bonds | Level 1
Financial assets
Total securities available for sale:	0	0
Recurring basis | Municipal bonds | Level 2
Financial assets
Total securities available for sale:	397,298	238,630
Recurring basis | Municipal bonds | Level 3
Financial assets
Total securities available for sale:	0	0
Recurring basis | Collateralized mortgage obligation: residential
Financial assets
Total securities available for sale:	9,984	24,338
Recurring basis | Collateralized mortgage obligation: residential | Level 1
Financial assets
Total securities available for sale:	0	0
Recurring basis | Collateralized mortgage obligation: residential | Level 2
Financial assets
Total securities available for sale:	9,984	24,338
Recurring basis | Collateralized mortgage obligation: residential | Level 3
Financial assets
Total securities available for sale:	0	0
Recurring basis | Mortgage-backed securities: residential
Financial assets
Total securities available for sale:	499,836	545,729
Recurring basis | Mortgage-backed securities: residential | Level 1
Financial assets
Total securities available for sale:	0	0
Recurring basis | Mortgage-backed securities: residential | Level 2
Financial assets
Total securities available for sale:	499,836	545,729
Recurring basis | Mortgage-backed securities: residential | Level 3
Financial assets
Total securities available for sale:	$ 0	$ 0