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BASIS OF PRESENTATION - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Jan. 01, 2018
Recent accounting pronouncements
Accumulated other comprehensive income	$ (2,514)	$ (1,609)
Retained earnings	554,363	563,593
ASU 2016-01
Recent accounting pronouncements
Equity investments that do not have readily determinable fair values			$ 20,100
Equity investments			600
ASU 2018-15 \| Early Adoption
Recent accounting pronouncements
Capitalized implementation costs	3,600	$ 1,200
Amortization of implementation costs	$ 100
Adjustment \| ASU 2016-01
Recent accounting pronouncements
Accumulated other comprehensive income			(200)
Retained earnings			200
Adjustment \| ASU 2018-02 \| Early Adoption
Recent accounting pronouncements
Accumulated other comprehensive income			(800)
Retained earnings			800
Valuation allowance			$ 800