Fair Value Measurements - Assets and liabilities recorded at fair value on recurring basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 1,150,885	$ 843,165
Assets measured at a fair value	1,247,716
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	88,205	56,707
Assets measured at a fair value		900,469
Derivative liability		86
Liabilities measured at a fair value	4,208	667
Derivative Financial Instruments, Liability | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	118
Interest Rate Caps | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	3,413	317
Derivative liability	3,574	312
Interest Rate Swap | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	516	203
U. S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	181,921	179,794
U. S. agency securities | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	181,921	179,794
Residential mortgage backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	825,001	543,852
Fair Value	88,205	56,707
Residential mortgage backed securities | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	825,001	543,852
Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	108,113	73,931
Municipal bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	108,113	73,931
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	35,850	10,733
Corporate bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	35,850	10,733
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value		34,855
U.S. Treasury | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value		34,855
Mortgage Banking Derivative | Recurring | Derivative Financial Instruments, Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	5,213	280
Mortgage Banking Derivative | Derivative Financial Instruments, Liability | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability		66
Fair Value, Inputs, Level 1 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Assets measured at a fair value	0	0
Derivative liability		0
Liabilities measured at a fair value	0	0
Fair Value, Inputs, Level 1 | Derivative Financial Instruments, Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Fair Value, Inputs, Level 1 | Interest Rate Caps | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Derivative liability	0	0
Fair Value, Inputs, Level 1 | Interest Rate Swap | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0	0
Fair Value, Inputs, Level 1 | U. S. agency securities | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0	0
Fair Value, Inputs, Level 1 | Residential mortgage backed securities | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0	0
Fair Value, Inputs, Level 1 | Municipal bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0	0
Fair Value, Inputs, Level 1 | Corporate bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0	0
Fair Value, Inputs, Level 1 | U.S. Treasury | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value		0
Fair Value, Inputs, Level 1 | Mortgage Banking Derivative | Recurring | Derivative Financial Instruments, Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Fair Value, Inputs, Level 1 | Mortgage Banking Derivative | Derivative Financial Instruments, Liability | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability		0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,149,385	832,432
Fair Value	88,205	56,707
Fair Value, Inputs, Level 2 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	88,205	56,707
Assets measured at a fair value	1,241,003	889,456
Derivative liability		86
Liabilities measured at a fair value	4,208	601
Fair Value, Inputs, Level 2 | Derivative Financial Instruments, Liability | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	118
Fair Value, Inputs, Level 2 | Interest Rate Caps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	3,413
Derivative liability	3,574	312
Fair Value, Inputs, Level 2 | Interest Rate Caps | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	3,413	317
Derivative liability	3,574	312
Fair Value, Inputs, Level 2 | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	516	203
Fair Value, Inputs, Level 2 | Interest Rate Swap | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	516	203
Fair Value, Inputs, Level 2 | U. S. agency securities | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	181,921	179,794
Fair Value, Inputs, Level 2 | Residential mortgage backed securities | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	825,001	543,852
Fair Value, Inputs, Level 2 | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value		0
Fair Value, Inputs, Level 2 | Municipal bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	108,113	73,931
Fair Value, Inputs, Level 2 | Corporate bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	34,350
Fair Value, Inputs, Level 2 | U.S. Treasury | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value		34,855
Fair Value, Inputs, Level 2 | Mortgage Banking Derivative | Recurring | Derivative Financial Instruments, Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Fair Value, Inputs, Level 2 | Mortgage Banking Derivative | Derivative Financial Instruments, Liability | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability		0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,500	10,931
Fair Value, Inputs, Level 3 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at a fair value	6,713	11,013
Liabilities measured at a fair value	0	66
Fair Value, Inputs, Level 3 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value		0
Fair Value, Inputs, Level 3 | Corporate bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,500	10,733
Fair Value, Inputs, Level 3 | Mortgage Banking Derivative | Recurring | Derivative Financial Instruments, Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	$ 5,213	280
Fair Value, Inputs, Level 3 | Mortgage Banking Derivative | Derivative Financial Instruments, Liability | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability		$ 66