Fair Value Measurements - Assets and liabilities recorded at fair value on recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investment securities	$ 977,570	$ 843,363
Derivative asset	4,306	311
Derivative liability	5,216	611
U. S. agency securities
Investment securities	131,286	179,794
Residential mortgage backed securities
Investment securities	716,643	543,852
Loans held for sale	79,084	56,707
Municipal bonds
Investment securities	94,713	73,931
Corporate bonds
Investment securities	34,730	10,733
U.S. Treasury
Investment securities		34,855
Other equity investments
Investment securities	198	198
Recurring
Other equity investments		198
Loans held for sale	79,084	56,707
Assets, Fair Value Disclosure	1,066,902	900,667
Derivative liability	136	86
Total liabilities measured at fair value on a recurring basis	5,533	667
Recurring | Interest Rate Swap
Derivative liability	910	203
Recurring | Interest Rate Caps
Derivative asset	4,233	317
Derivative liability	4,487	312
Recurring | U. S. agency securities
Investment securities	131,286	179,794
Recurring | Residential mortgage backed securities
Investment securities	716,643	543,852
Recurring | Municipal bonds
Investment securities	94,713	73,931
Recurring | Corporate bonds
Investment securities	34,730	10,733
Recurring | U.S. Treasury
Investment securities		34,855
Recurring | Other equity investments
Other equity investments	198
Recurring | Mortgage Banking Derivative | Derivative Financial Instruments, Liability
Derivative liability		66
Recurring | Mortgage Banking Derivative | Derivative Financial Instruments, Assets
Derivative asset		280
Recurring | Mortgage Banking Derivative | Interest Rate Swap
Derivative asset	6,015
Recurring | Fair Value, Inputs, Level 1
Other equity investments		0
Loans held for sale	0	0
Assets, Fair Value Disclosure	0	0
Derivative liability	0	0
Total liabilities measured at fair value on a recurring basis	0	0
Recurring | Fair Value, Inputs, Level 1 | Interest Rate Swap
Derivative liability	0	0
Recurring | Fair Value, Inputs, Level 1 | Interest Rate Caps
Derivative asset	0	0
Derivative liability	0	0
Recurring | Fair Value, Inputs, Level 1 | U. S. agency securities
Investment securities	0	0
Recurring | Fair Value, Inputs, Level 1 | Residential mortgage backed securities
Investment securities	0	0
Recurring | Fair Value, Inputs, Level 1 | Municipal bonds
Investment securities	0	0
Recurring | Fair Value, Inputs, Level 1 | Corporate bonds
Investment securities	0	0
Recurring | Fair Value, Inputs, Level 1 | U.S. Treasury
Investment securities		0
Recurring | Fair Value, Inputs, Level 1 | Other equity investments
Other equity investments	0
Recurring | Fair Value, Inputs, Level 1 | Mortgage Banking Derivative | Derivative Financial Instruments, Liability
Derivative liability		0
Recurring | Fair Value, Inputs, Level 1 | Mortgage Banking Derivative | Derivative Financial Instruments, Assets
Derivative asset		0
Recurring | Fair Value, Inputs, Level 2
Loans held for sale	79,084	56,707
Assets, Fair Value Disclosure	1,059,189	889,456
Derivative liability	136	86
Total liabilities measured at fair value on a recurring basis	5,533	601
Recurring | Fair Value, Inputs, Level 2 | Interest Rate Swap
Derivative liability	910	203
Recurring | Fair Value, Inputs, Level 2 | Interest Rate Caps
Derivative asset	4,233	317
Derivative liability	4,487	312
Recurring | Fair Value, Inputs, Level 2 | U. S. agency securities
Investment securities	131,286	179,794
Recurring | Fair Value, Inputs, Level 2 | Residential mortgage backed securities
Investment securities	716,643	543,852
Recurring | Fair Value, Inputs, Level 2 | Municipal bonds
Investment securities	94,713	73,931
Recurring | Fair Value, Inputs, Level 2 | Corporate bonds
Investment securities	33,230
Recurring | Fair Value, Inputs, Level 2 | U.S. Treasury
Investment securities		34,855
Recurring | Fair Value, Inputs, Level 2 | Other equity investments
Other equity investments	0
Recurring | Fair Value, Inputs, Level 3
Other equity investments		198
Assets, Fair Value Disclosure	7,713	11,211
Derivative liability	0
Total liabilities measured at fair value on a recurring basis	0	66
Recurring | Fair Value, Inputs, Level 3 | Interest Rate Swap
Derivative liability	0
Recurring | Fair Value, Inputs, Level 3 | Interest Rate Caps
Derivative liability	0
Recurring | Fair Value, Inputs, Level 3 | Corporate bonds
Investment securities	1,500	10,733
Recurring | Fair Value, Inputs, Level 3 | Other equity investments
Other equity investments	198
Recurring | Fair Value, Inputs, Level 3 | Mortgage Banking Derivative | Derivative Financial Instruments, Liability
Derivative liability		66
Recurring | Fair Value, Inputs, Level 3 | Mortgage Banking Derivative | Derivative Financial Instruments, Assets
Derivative asset		$ 280
Recurring | Fair Value, Inputs, Level 3 | Mortgage Banking Derivative | Interest Rate Swap
Derivative asset	$ 6,015