SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Topic 326 adoption Impact (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment	$ 58,299		$ 41,772
Off-Balance Sheet, Credit Loss, Liability			1,065
Allowance for credit losses	60,606		42,837	$ 44,536	$ 42,913
Consumer loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			12,683
Allowance for credit losses	21,478		13,293	15,981	15,929
Consumer loans [Member] | Single family [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			6,450
Allowance for credit losses	8,587		6,450	8,190	8,217
Consumer loans [Member] | Home equity and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			6,233
Allowance for credit losses	12,891		6,843	7,791	7,712
Commercial loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses			22,943
Commercial loans [Member] | Non-owner occupied commercial real estate [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			7,245
Allowance for credit losses	9,027		7,249	6,176	5,496
Commercial loans [Member] | Multifamily [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			7,015
Allowance for credit losses	4,275		7,015	6,360	5,754
Commercial loans [Member] | Multifamily Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			2,848
Allowance for credit losses	3,658		2,996
Commercial loans [Member] | Commercial Real Estate Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			624
Allowance for credit losses	396		627
Commercial loans [Member] | Single Family Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			3,800
Allowance for credit losses	7,352		3,940
Commercial loans [Member] | Single Family Construction To Permanent [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			1,003
Allowance for credit losses	1,985		1,116
Commercial loans [Member] | Owner occupied commercial real estate [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			3,639
Allowance for credit losses	4,166		3,640	3,304	3,282
Commercial loans [Member] | Commercial business [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			2,915
Allowance for credit losses	8,269		2,961	3,064	2,913
Real Estate Sector [Member] | Commercial loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			22,535
Allowance for credit losses	26,693		22,943	22,187	20,789
Commercial and Industrial Sector [Member] | Commercial loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment			6,554
Allowance for credit losses	$ 12,435		6,601	$ 6,368	6,195
Cumulative Effect, Period Of Adoption, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		$ 1,843
Off-Balance Sheet, Credit Loss, Liability		1,897
Allowance for credit losses		3,740	$ 3,740		$ 0
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Consumer loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		5,103
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Consumer loans [Member] | Single family [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		468
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Consumer loans [Member] | Home equity and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		4,635
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Non-owner occupied commercial real estate [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		(3,392)
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Multifamily [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		(2,977)
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Multifamily Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		693
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Commercial Real Estate Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		(115)
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Single Family Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		4,280
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Single Family Construction To Permanent [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		200
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Owner occupied commercial real estate [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		(2,459)
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial loans [Member] | Commercial business [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		510
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Real Estate Sector [Member] | Commercial loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		(1,311)
Cumulative Effect, Period Of Adoption, Adjustment [Member] | Commercial and Industrial Sector [Member] | Commercial loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		(1,949)
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		43,615
Off-Balance Sheet, Credit Loss, Liability		2,962
Allowance for credit losses		46,577
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Consumer loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		17,786
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Consumer loans [Member] | Single family [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		6,918
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Consumer loans [Member] | Home equity and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		10,868
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Non-owner occupied commercial real estate [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		3,853
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Multifamily [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		4,038
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Multifamily Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		3,541
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Commercial Real Estate Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		509
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Single Family Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		8,080
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Single Family Construction To Permanent [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		1,203
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Owner occupied commercial real estate [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		1,180
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial loans [Member] | Commercial business [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		3,425
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Real Estate Sector [Member] | Commercial loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		21,224
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member] | Commercial and Industrial Sector [Member] | Commercial loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on loans held for investment		$ 4,605