CONSOLIDATED FINANCIAL STATEMENT DETAILS - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 402,914	$ 336,984	$ 279,489	$ 221,521
Restricted cash included in other current assets	1,421	1,417	0	0
Restricted cash included in other non-current assets	403	420	433	0
Total cash, cash equivalents, and restricted cash as shown on the consolidated statement of cash flows	$ 404,738	$ 338,821	$ 279,922	$ 221,521