CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities
Net loss	$ (20,863)	$ (41,629)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	9,010	7,092
Amortization of debt discount and issuance costs	960	135
Accretion of premium on short-term investments	569	577
Deferred income taxes	504	32,534
Stock-based compensation	17,301	15,260
Income tax charge (benefit) from stock-based compensation	249	(266)
Changes in operating assets and liabilities:
Accounts receivable, net	1,527	(4,237)
Prepaid expenses and other	(174)	734
Accounts payable	2,581	(1,087)
Accrued taxes	1,110	85
Accrued compensation and benefits	1,227	(5,094)
Accrued liabilities and other	763	5,050
Net cash provided by operating activities	14,764	9,154
Cash flows from investing activities
Acquisition of property and equipment	(3,108)	(17,049)
Purchases of short-term investments	(78,502)	(31,100)
Sales of short-term investments	5,336	52,050
Maturities of short-term investments	2,000	21,415
Net cash used in (provided by) investing activities	(74,274)	25,316
Cash flows from financing activities
Proceeds from issuance of convertible notes	150,000	0
Issuance costs related to the issuance of convertible senior notes	(4,350)	0
Payments of convertible note hedges	(31,408)	0
Proceeds from the issuance of warrants	21,763	0
Repayment on capital leases obligations	(245)	(234)
Proceeds from common stock issuances	21,969	10,279
Income tax charge (benefit) from stock-based compensation	(249)	266
Net cash provided by financing activities	157,480	10,311
Net increase in cash and cash equivalents	97,970	44,781
Effect of exchange rate changes on cash and cash equivalents	136	(487)
Cash and cash equivalents at beginning of period	76,568	65,983
Cash and cash equivalents at end of period	$ 174,674	$ 110,277