Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Available-for-sale Securities, Current	$ 268,251	$ 195,702
Current assets:
Cash and cash equivalents	366,303	118,989
Accounts receivable, net	108,339	78,163
Current portion of deferred commissions	31,123	14,979
Prepaid expenses and other current assets	23,733	14,256
Total current assets	797,749	422,089
Deferred commissions, less current portion	21,318	11,296
Long-term investments	255,356	0
Property and equipment, net	75,560	42,342
Intangible Assets, Net	5,796	596
Goodwill	8,724	0
Other assets	3,973	1,791
Total assets	1,168,476	478,114
Current liabilities:
Accounts payable	7,405	9,604
Accrued expenses and other current liabilities	68,130	48,059
Current portion of deferred revenue	252,553	153,964
Total current liabilities	328,088	211,627
Deferred Revenue, Noncurrent	14,169	16,397
Convertible senior notes, net	414,777	0
Other long-term liabilities	17,183	6,685
Total liabilities	774,217	234,709
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock $0.001 par value; 600,000,000 shares authorized; 140,354,605 and 126,367,700 shares issued and outstanding at December 31, 2013 and 2012, respectively	140	126
Additional paid-in capital	573,791	348,803
Accumulated other comprehensive loss	(476)	(36)
Accumulated deficit	(179,196)	(105,488)
Total stockholders’ equity	394,259	243,405
Total liabilities and stockholders’ equity	$ 1,168,476	$ 478,114