Fair Value Measurements - Assets and liabilities recorded at fair value on recurring basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	$ 1,368,909	$ 1,150,885
U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	275,535	181,921
Residential mortgage backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	932,619	825,001
Loans held for sale	142,196	88,205
Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	107,122	108,113
Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	53,633	35,850
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	142,196	88,205
Assets measured at fair value on a nonrecurring basis	1,517,226	1,247,716
Derivative liability	78	118
Total liabilities measured at fair value on a recurring basis	3,697	4,208
Recurring \| Interest rate swap derivatives
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability	133	516
Recurring \| Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	3,607	3,413
Derivative liability	3,486	3,574
Recurring \| U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	275,535	181,921
Recurring \| Residential mortgage backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	932,619	825,001
Recurring \| Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	107,122	108,113
Recurring \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	53,633	35,850
Recurring \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	2,514	5,213
Recurring \| Fair Value, Inputs, Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	0
Assets measured at fair value on a nonrecurring basis	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 derivatives
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	0	0
Derivative liability	0	0
Recurring \| Fair Value, Inputs, Level 1 \| U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Residential mortgage backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	0	0
Recurring \| Fair Value, Inputs, Level 1 \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	0	0
Recurring \| Fair Value, Inputs, Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	142,196	88,205
Assets measured at fair value on a nonrecurring basis	1,513,212	1,241,003
Derivative liability	78	118
Total liabilities measured at fair value on a recurring basis	3,697	4,208
Recurring \| Fair Value, Inputs, Level 2 \| Interest rate swap derivatives
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability	133	516
Recurring \| Fair Value, Inputs, Level 2 \| Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	3,607	3,413
Derivative liability	3,486	3,574
Recurring \| Fair Value, Inputs, Level 2 \| U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	275,535	181,921
Recurring \| Fair Value, Inputs, Level 2 \| Residential mortgage backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	932,619	825,001
Recurring \| Fair Value, Inputs, Level 2 \| Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	107,122	108,113
Recurring \| Fair Value, Inputs, Level 2 \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	52,133	34,350
Recurring \| Fair Value, Inputs, Level 2 \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	0	0
Recurring \| Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets measured at fair value on a nonrecurring basis	4,014	6,713
Total liabilities measured at fair value on a recurring basis	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	1,500	1,500
Recurring \| Fair Value, Inputs, Level 3 \| Mortgage banking derivatives \| Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	$ 2,514	$ 5,213

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value of financial and nonfinancial obligations.

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