Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Cash flows from operating activities:
Net loss	$ (13,358)		$ (5,640)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	4,364		2,046
Amortization of premiums on short-term investments, net	1,095		0
Amortization of deferred commissions	5,366		2,343
Stock-based compensation	12,046		3,918
Tax benefit from exercise of stock options	(1,851)		(960)
Bad debt expense	283		0
Lease abandonment costs	298		0
Changes in operating assets and liabilities:
Accounts receivable	(2,938)		2,058
Deferred commissions	(9,269)		(5,253)
Prepaid expenses and other current assets	3,918		4,172
Other assets	(230)		(74)
Accounts payable	(1,471)		1,433
Accrued expenses and other current liabilities	(9,012)		1,045
Deferred revenue	25,729		11,022
Other long-term liabilities	53		(31)
Net cash provided by operating activities	15,023		16,079
Cash flows from investing activities:
Purchases of property and equipment	(10,415)		(8,558)
Purchases of short-term investments	(55,946)		(15,344)
Maturities of short-term investments	55,350	[1]	0
Restricted cash	0		8
Net cash used in investing activities	(11,011)		(23,894)
Cash flows from financing activities:
Net proceeds from follow-on offering	(698)		0
Proceeds from exercise of stock options	21,468		1,301
Proceeds from early exercise of stock options	0		887
Tax benefit from exercise of stock options	1,851		960
Net proceeds from issuance of common stock	0		17,848
Purchases of common stock and restricted stock from stockholders	0		(1,069)
Net cash provided by financing activities	22,621		19,927
Foreign currency effect on cash and cash equivalents	(840)		(60)
Net increase in cash and cash equivalents	25,793		12,052
Cash and cash equivalents at beginning of period	118,989		68,088
Cash and cash equivalents at end of period	144,782		80,140
Supplemental disclosures of non-cash investing activities:
Property and equipment included in accounts payable and accrued expenses	$ 6,157		$ 3,078

[1] Maturities of short-term investments include the effect of the correction of an immaterial error of $3.0 million related to securities that were improperly classified as short-term investments instead of cash and cash equivalents as of December 31, 2012.