CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (41,140)	$ (187,083)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	13,424	15,027
Stock-based compensation	36,224	30,613
Expense related to senior note conversions		54,130
Other, net	87	71
Unrealized (gain) loss on long term investments	(22,679)	5,814
Change in fair value of acquisition-related contingent consideration	6,685	7,356
Changes in operating assets and liabilities:
Accounts receivable	46,109	(96,217)
Prepaid expenses and other assets	(18,922)	(25,094)
Inventory	1,879	790
Accounts payable	6,444	10,728
Accrued and other liabilities	(7,273)	10,227
Net cash provided by (used in) operating activities	20,838	(173,638)
Cash flows from investing activities:
Purchase of long term investments	(8,937)	(123,891)
Capital expenditures	(12,590)	(20,967)
Purchases of marketable securities	(38,033)	(106,271)
Sale and maturities of marketable securities	31,032	112,310
Net cash used in investing activities	(28,528)	(138,819)
Cash flows from financing activities:
Proceeds from issuance of common stock under stock plans	2,595	33,736
Cash paid in connection with senior note conversions		(8,097)
Payment of contingent consideration		(3,679)
Net cash provided by financing activities	2,595	21,960
Effect of exchange rates on cash and cash equivalents	35	(7)
Net decrease in cash, cash equivalents, restricted cash and investments	(5,060)	(290,504)
Cash, cash equivalents, restricted cash and investments at beginning of period	900,434	653,229
Cash, cash equivalents, restricted cash and investments at end of period	895,374	362,725
Supplemental Schedule of Cash Flow Information
Income taxes paid	52	2,244
Unpaid purchases of property and equipment		9,139
Convertible Senior Notes 0.375 Percent Due 2018
Supplemental Schedule of Cash Flow Information
Reclassification to common stock and additional paid in capital in connection with conversions or exchange of convertible senior notes	$ 27	334,162
Convertible Senior Notes 1.25 Percent Due 2020
Supplemental Schedule of Cash Flow Information
Reclassification to common stock and additional paid in capital in connection with conversions or exchange of convertible senior notes		$ 328,382