ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Loss
Balance at January 1	$ 993,346
Other comprehensive (loss) income before reclassifications	(4,041)	$ 3,980	$ (657)
Amounts reclassified to earnings	(52)	(27)
Net current period other comprehensive (loss) income	(4,093)	3,953	(657)
Balance at December 31	1,312,941	993,346
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Loss
Balance at January 1	2,232	(1,721)	(1,064)
Other comprehensive (loss) income before reclassifications	(4,044)	3,980	(657)
Amounts reclassified to earnings	(52)	(27)
Net current period other comprehensive (loss) income	(4,096)	3,953	(657)
Balance at December 31	(1,864)	2,232	(1,721)
Unrealized Gains On Available-For-Sale Debt Securities
Accumulated Other Comprehensive Loss
Balance at January 1	0
Other comprehensive (loss) income before reclassifications	3
Amounts reclassified to earnings
Net current period other comprehensive (loss) income	3
Balance at December 31	3	0
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Loss
Balance at January 1	2,232	(1,721)	(1,064)
Balance at December 31	$ (1,861)	$ 2,232	$ (1,721)