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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Recent accounting pronouncements
Accumulated other comprehensive income	$ 278	$ (3,282)
Retained earnings	516,901	541,890
Valuation allowance	$ 31,014	39,406
Cumulative Effect, Period of Adoption, Adjustment \| ASU 2016-13
Recent accounting pronouncements
Retained earnings		$ 0
Cumulative Effect, Period of Adoption, Adjustment \| ASU 2016-01
Recent accounting pronouncements
Accumulated other comprehensive income			$ (200)
Retained earnings			200
Cumulative Effect, Period of Adoption, Adjustment \| ASU 2018-02 \| Early Adoption
Recent accounting pronouncements
Accumulated other comprehensive income			(800)
Retained earnings			800
Valuation allowance			800
Cumulative Effect, Period of Adoption, Adjusted Balance \| ASU 2016-01
Recent accounting pronouncements
Equity investments that do not have readily determinable fair values			20,100
Equity investments			$ 600