Fair Value Measurements - Assets and liabilities recorded at fair value on recurring basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	$ 1,680,832	$ 1,150,885
U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	357,311	181,921
Residential mortgage backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	1,146,322	825,001
Loans held for sale	55,949	88,205
Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	100,277	108,113
Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	76,922	35,850
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	55,949	88,205
Assets measured at fair value on a nonrecurring basis	1,743,397	1,247,716
Derivative liability	74	118
Total liabilities measured at fair value on a recurring basis	5,689	4,208
Recurring | Interest rate swap derivatives
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability	0	516
Recurring | Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	5,437	3,413
Derivative liability	5,615	3,574
Recurring | U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	357,311	181,921
Recurring | Residential mortgage backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	1,146,322	825,001
Recurring | Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	100,277	108,113
Recurring | Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	76,922	35,850
Recurring | Mortgage banking derivatives | Derivative Financial Instruments, Assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	1,179	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	55,949	88,205
Assets measured at fair value on a nonrecurring basis	1,740,718	1,241,003
Derivative liability	74	118
Total liabilities measured at fair value on a recurring basis	5,689	4,208
Recurring | Fair Value, Inputs, Level 2 | Interest rate swap derivatives
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability	0	516
Recurring | Fair Value, Inputs, Level 2 | Interest rate caps
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	5,437	3,413
Derivative liability	5,615	3,574
Recurring | Fair Value, Inputs, Level 2 | U. S. agency securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	357,311	181,921
Recurring | Fair Value, Inputs, Level 2 | Residential mortgage backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	1,146,322	825,001
Recurring | Fair Value, Inputs, Level 2 | Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	100,277	108,113
Recurring | Fair Value, Inputs, Level 2 | Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities	75,422	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	2,679	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	$ 1,179	$ 5,213