CONSOLIDATED FINANCIAL STATEMENT DETAILS - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 345,351	$ 336,984	$ 228,744	$ 221,521
Restricted cash included in other current assets	1,419	1,417	0	0
Restricted cash included in other assets	416	420	0	0
Total cash, cash equivalents, and restricted cash as shown on the consolidated statement of cash flows	$ 347,186	$ 338,821	$ 228,744	$ 221,521