FAIR VALUE MEASUREMENT - Schedule of Fair Value Hierarchy Measurement (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Investment securities available for sale	$ 1,044,859	$ 1,072,093
Single family mortgage servicing rights	62,352
Derivative assets	18,772	27,639
Liabilities:
Derivative liabilities	3,601	2,785
Residential mortgage-backed securities
Assets:
Investment securities available for sale	43,238	51,046
Commercial mortgage-backed securities
Assets:
Investment securities available for sale	43,025	45,184
Municipal bonds
Assets:
Investment securities available for sale	561,011	564,703
Corporate debt securities
Assets:
Investment securities available for sale	14,936	15,222
Agency debentures
Assets:
Investment securities available for sale		1,846
Recurring
Assets:
Fair value of loans held for sale	241,600	194,643
Fair value of loans held for investment	4,324	7,108
Single family mortgage servicing rights	62,352	49,966
Total assets	1,381,518	1,359,699
Liabilities:
Total liabilities	23,197	24,232
Recurring \| Residential mortgage-backed securities
Assets:
Investment securities available for sale	43,238	51,046
Recurring \| Commercial mortgage-backed securities
Assets:
Investment securities available for sale	43,025	45,184
Recurring \| Collateralized mortgage obligations residential
Assets:
Investment securities available for sale	230,498	234,909
Recurring \| Collateralized mortgage obligations commercial
Assets:
Investment securities available for sale	152,151	159,183
Recurring \| Municipal bonds
Assets:
Investment securities available for sale	561,011	564,703
Recurring \| Corporate debt securities
Assets:
Investment securities available for sale	14,936	15,222
Recurring \| Agency debentures
Assets:
Investment securities available for sale		1,846
Recurring \| Eurodollar futures
Assets:
Derivative assets	6
Liabilities:
Derivative liabilities		4
Recurring \| Forward sale commitments
Assets:
Derivative assets	13,509	1,035
Liabilities:
Derivative liabilities	6,215	3,714
Recurring \| Interest rate lock commitments
Assets:
Derivative assets	6,686	17,395
Liabilities:
Derivative liabilities	198	3
Recurring \| Interest rate swaps
Assets:
Derivative assets	8,182	17,459
Liabilities:
Derivative liabilities	16,784	20,511
Level 1 \| Recurring
Assets:
Fair value of loans held for sale	0	0
Fair value of loans held for investment	0	0
Single family mortgage servicing rights	0	0
Total assets	6	0
Liabilities:
Total liabilities	0	4
Level 1 \| Recurring \| Residential mortgage-backed securities
Assets:
Investment securities available for sale	0	0
Level 1 \| Recurring \| Commercial mortgage-backed securities
Assets:
Investment securities available for sale	0	0
Level 1 \| Recurring \| Collateralized mortgage obligations residential
Assets:
Investment securities available for sale	0	0
Level 1 \| Recurring \| Collateralized mortgage obligations commercial
Assets:
Investment securities available for sale	0	0
Level 1 \| Recurring \| Municipal bonds
Assets:
Investment securities available for sale	0	0
Level 1 \| Recurring \| Corporate debt securities
Assets:
Investment securities available for sale	0	0
Level 1 \| Recurring \| Agency debentures
Assets:
Investment securities available for sale		0
Level 1 \| Recurring \| Eurodollar futures
Assets:
Derivative assets	6
Liabilities:
Derivative liabilities		4
Level 1 \| Recurring \| Forward sale commitments
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 1 \| Recurring \| Interest rate lock commitments
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 1 \| Recurring \| Interest rate swaps
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 2 \| Recurring
Assets:
Fair value of loans held for sale	241,600	194,643
Fair value of loans held for investment	0	0
Single family mortgage servicing rights	0	0
Total assets	1,305,660	1,282,520
Liabilities:
Total liabilities	22,999	24,225
Level 2 \| Recurring \| Residential mortgage-backed securities
Assets:
Investment securities available for sale	40,828	48,417
Level 2 \| Recurring \| Commercial mortgage-backed securities
Assets:
Investment securities available for sale	43,025	45,184
Level 2 \| Recurring \| Collateralized mortgage obligations residential
Assets:
Investment securities available for sale	230,498	234,909
Level 2 \| Recurring \| Collateralized mortgage obligations commercial
Assets:
Investment securities available for sale	152,151	159,183
Level 2 \| Recurring \| Municipal bonds
Assets:
Investment securities available for sale	561,011	564,703
Level 2 \| Recurring \| Corporate debt securities
Assets:
Investment securities available for sale	14,856	15,141
Level 2 \| Recurring \| Agency debentures
Assets:
Investment securities available for sale		1,846
Level 2 \| Recurring \| Eurodollar futures
Assets:
Derivative assets	0
Liabilities:
Derivative liabilities		0
Level 2 \| Recurring \| Forward sale commitments
Assets:
Derivative assets	13,509	1,035
Liabilities:
Derivative liabilities	6,215	3,714
Level 2 \| Recurring \| Interest rate lock commitments
Assets:
Derivative assets		0
Liabilities:
Derivative liabilities	0	0
Level 2 \| Recurring \| Interest rate swaps
Assets:
Derivative assets	8,182	17,459
Liabilities:
Derivative liabilities	16,784	20,511
Level 3 \| Recurring
Assets:
Investment securities available for sale	2,490	2,710
Fair value of loans held for sale	0	0
Fair value of loans held for investment	4,324	7,108
Single family mortgage servicing rights	62,352	49,966
Total assets	75,852	77,179
Liabilities:
Total liabilities	198	3
Level 3 \| Recurring \| Residential mortgage-backed securities
Assets:
Investment securities available for sale	2,410	2,629
Level 3 \| Recurring \| Commercial mortgage-backed securities
Assets:
Investment securities available for sale	0	0
Level 3 \| Recurring \| Collateralized mortgage obligations residential
Assets:
Investment securities available for sale	0	0
Level 3 \| Recurring \| Collateralized mortgage obligations commercial
Assets:
Investment securities available for sale	0	0
Level 3 \| Recurring \| Municipal bonds
Assets:
Investment securities available for sale	0	0
Level 3 \| Recurring \| Corporate debt securities
Assets:
Investment securities available for sale	80	81
Level 3 \| Recurring \| Agency debentures
Assets:
Investment securities available for sale		0
Level 3 \| Recurring \| Eurodollar futures
Assets:
Derivative assets	0
Liabilities:
Derivative liabilities		0
Level 3 \| Recurring \| Forward sale commitments
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 3 \| Recurring \| Interest rate lock commitments
Assets:
Derivative assets	6,686	17,395
Liabilities:
Derivative liabilities	198	3
Level 3 \| Recurring \| Interest rate swaps
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities		$ 0

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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value of financial and nonfinancial obligations.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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