THE COMPANY AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 279,489	$ 221,521	$ 59,543	$ 36,377
Restricted cash included in other current assets	0	0	190	0
Restricted cash included in other assets	433	0	0	10,548
Total cash, cash equivalents and restricted cash as shown on the consolidated statement of cash flows	$ 279,922	$ 221,521	$ 59,733	$ 46,925