FAIR VALUE MEASUREMENT - Schedule of Fair Value Hierarchy Measurement (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Investment securities available for sale	$ 1,167,499	$ 938,778
Single family mortgage servicing rights	47,804
Derivative assets	33,803	8,797
Liabilities:
Derivative liabilities	3,665	2,338
Residential mortgage-backed securities [Member]
Assets:
Investment securities available for sale	69,581	91,695
Commercial mortgage-backed securities [Member]
Assets:
Investment securities available for sale	46,796	38,025
Municipal bonds [Member]
Assets:
Investment securities available for sale	567,165	341,318
Corporate debt securities [Member]
Assets:
Investment securities available for sale	10,096	18,661
Agency debentures [Member]
Assets:
Investment securities available for sale	12,365
Recurring [Member]
Assets:
Fair value of loans held for sale	284,865	105,458
Fair value of loans held for investment	5,847	3,468
Single family mortgage servicing rights	47,804	68,109
Total assets	1,557,798	1,146,024
Liabilities:
Total liabilities	30,164	11,439
Recurring [Member] \| Residential mortgage-backed securities [Member]
Assets:
Investment securities available for sale	69,581	91,695
Recurring [Member] \| Commercial mortgage-backed securities [Member]
Assets:
Investment securities available for sale	46,796	38,025
Recurring [Member] \| Collateralized mortgage obligations residential [Member]
Assets:
Investment securities available for sale	294,703	291,618
Recurring [Member] \| Collateralized mortgage obligations commercial [Member]
Assets:
Investment securities available for sale	165,488	156,154
Recurring [Member] \| Municipal bonds [Member]
Assets:
Investment securities available for sale	567,165	341,318
Recurring [Member] \| Corporate debt securities [Member]
Assets:
Investment securities available for sale	10,096	18,661
Recurring [Member] \| US treasury securities [Member]
Assets:
Investment securities available for sale	1,305	1,307
Recurring [Member] \| Agency debentures [Member]
Assets:
Investment securities available for sale	12,365
Recurring [Member] \| Eurodollar futures [Member]
Assets:
Derivative assets		3
Liabilities:
Derivative liabilities	4
Recurring [Member] \| Forward sale commitments [Member]
Assets:
Derivative assets	978	830
Liabilities:
Derivative liabilities	3,765	492
Recurring [Member] \| Interest rate lock commitments [Member]
Assets:
Derivative assets	17,967	2,281
Liabilities:
Derivative liabilities		58
Recurring [Member] \| Interest rate swaps [Member]
Assets:
Derivative assets	32,838	27,097
Liabilities:
Derivative liabilities	26,395	10,889
Level 1 [Member] \| Recurring [Member]
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	0	3
Liabilities:
Total liabilities	0	0
Level 1 [Member] \| Recurring [Member] \| Residential mortgage-backed securities [Member]
Assets:
Investment securities available for sale	0	0
Level 1 [Member] \| Recurring [Member] \| Commercial mortgage-backed securities [Member]
Assets:
Investment securities available for sale	0	0
Level 1 [Member] \| Recurring [Member] \| Collateralized mortgage obligations residential [Member]
Assets:
Investment securities available for sale	0	0
Level 1 [Member] \| Recurring [Member] \| Collateralized mortgage obligations commercial [Member]
Assets:
Investment securities available for sale	0	0
Level 1 [Member] \| Recurring [Member] \| Municipal bonds [Member]
Assets:
Investment securities available for sale	0	0
Level 1 [Member] \| Recurring [Member] \| Corporate debt securities [Member]
Assets:
Investment securities available for sale	0	0
Level 1 [Member] \| Recurring [Member] \| US treasury securities [Member]
Assets:
Investment securities available for sale	0	0
Level 1 [Member] \| Recurring [Member] \| Agency debentures [Member]
Assets:
Investment securities available for sale	0
Level 1 [Member] \| Recurring [Member] \| Eurodollar futures [Member]
Assets:
Derivative assets		3
Liabilities:
Derivative liabilities
Level 1 [Member] \| Recurring [Member] \| Forward sale commitments [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 1 [Member] \| Recurring [Member] \| Interest rate lock commitments [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities		0
Level 1 [Member] \| Recurring [Member] \| Interest rate swaps [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 2 [Member] \| Recurring [Member]
Assets:
Fair value of loans held for sale	284,865	105,458
Fair value of loans held for investment	0	0
Single family mortgage servicing rights	0	0
Total assets	1,483,320	1,070,211
Liabilities:
Total liabilities	30,164	11,381
Level 2 [Member] \| Recurring [Member] \| Residential mortgage-backed securities [Member]
Assets:
Investment securities available for sale	66,805	89,831
Level 2 [Member] \| Recurring [Member] \| Commercial mortgage-backed securities [Member]
Assets:
Investment securities available for sale	46,796	38,025
Level 2 [Member] \| Recurring [Member] \| Collateralized mortgage obligations residential [Member]
Assets:
Investment securities available for sale	294,703	291,618
Level 2 [Member] \| Recurring [Member] \| Collateralized mortgage obligations commercial [Member]
Assets:
Investment securities available for sale	165,488	156,154
Level 2 [Member] \| Recurring [Member] \| Municipal bonds [Member]
Assets:
Investment securities available for sale	567,165	341,318
Level 2 [Member] \| Recurring [Member] \| Corporate debt securities [Member]
Assets:
Investment securities available for sale	10,012	18,573
Level 2 [Member] \| Recurring [Member] \| US treasury securities [Member]
Assets:
Investment securities available for sale	1,305	1,307
Level 2 [Member] \| Recurring [Member] \| Agency debentures [Member]
Assets:
Investment securities available for sale	12,365
Level 2 [Member] \| Recurring [Member] \| Eurodollar futures [Member]
Assets:
Derivative assets		0
Liabilities:
Derivative liabilities	4
Level 2 [Member] \| Recurring [Member] \| Forward sale commitments [Member]
Assets:
Derivative assets	978	830
Liabilities:
Derivative liabilities	3,765	492
Level 2 [Member] \| Recurring [Member] \| Interest rate lock commitments [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities		0
Level 2 [Member] \| Recurring [Member] \| Interest rate swaps [Member]
Assets:
Derivative assets	32,838	27,097
Liabilities:
Derivative liabilities	26,395	10,889
Level 3 [Member] \| Recurring [Member]
Assets:
Investment securities available for sale	2,861	1,952
Fair value of loans held for sale	0	0
Fair value of loans held for investment	5,847	3,468
Single family mortgage servicing rights	47,804	68,109
Total assets	74,478	75,810
Liabilities:
Total liabilities	0	58
Level 3 [Member] \| Recurring [Member] \| Residential mortgage-backed securities [Member]
Assets:
Investment securities available for sale	2,776	1,864
Level 3 [Member] \| Recurring [Member] \| Commercial mortgage-backed securities [Member]
Assets:
Investment securities available for sale	0	0
Level 3 [Member] \| Recurring [Member] \| Collateralized mortgage obligations residential [Member]
Assets:
Investment securities available for sale	0	0
Level 3 [Member] \| Recurring [Member] \| Collateralized mortgage obligations commercial [Member]
Assets:
Investment securities available for sale	0	0
Level 3 [Member] \| Recurring [Member] \| Municipal bonds [Member]
Assets:
Investment securities available for sale	0	0
Level 3 [Member] \| Recurring [Member] \| Corporate debt securities [Member]
Assets:
Investment securities available for sale	84	88
Level 3 [Member] \| Recurring [Member] \| US treasury securities [Member]
Assets:
Investment securities available for sale	0	0
Level 3 [Member] \| Recurring [Member] \| Agency debentures [Member]
Assets:
Investment securities available for sale	0
Level 3 [Member] \| Recurring [Member] \| Eurodollar futures [Member]
Assets:
Derivative assets		0
Liabilities:
Derivative liabilities	0
Level 3 [Member] \| Recurring [Member] \| Forward sale commitments [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Level 3 [Member] \| Recurring [Member] \| Interest rate lock commitments [Member]
Assets:
Derivative assets	17,967	2,281
Liabilities:
Derivative liabilities		58
Level 3 [Member] \| Recurring [Member] \| Interest rate swaps [Member]
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	$ 0	$ 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, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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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 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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