Significant Accounting Policies - Impact of Adoption of ASU 2014-09 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017		Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net revenues	$ 697,192	$ 662,677	[1]
Total cost of net revenues	108,286	102,458
Gross margin	588,906	560,219
Total operating expenses	423,343	437,575
Income from operations	165,563	122,644
Net income	$ 144,259	$ 27,621
Basic earnings per share (in dollars per share)	$ 1.04	$ 0.18
Diluted earnings per share (in dollars per share)	$ 0.99	$ 0.17
Contract assets	$ 7,307
Contract acquisition costs	83,806
Deferred tax assets, net	114,277				$ 152,362
Total assets	5,137,477				5,820,176
Deferred tax liabilities	60,025
Current portion of deferred revenues	1,204,199				1,308,474
Long-term portion of deferred revenues	480,985				555,769
Total liabilities	4,614,099
Retained earnings	3,786,521				$ 3,509,484
Balances without adoption of ASC 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net revenues	707,324
Total cost of net revenues	108,126
Gross margin	599,198
Total operating expenses	426,684
Income from operations	172,514
Net income	$ 150,902
Basic earnings per share (in dollars per share)	$ 1.08
Diluted earnings per share (in dollars per share)	$ 1.03
Contract assets	$ 0
Contract acquisition costs	14,233
Deferred tax assets, net	144,137
Total assets	5,090,457
Deferred tax liabilities	46,946
Current portion of deferred revenues	1,255,308
Long-term portion of deferred revenues	519,683
Total liabilities	4,690,827
Retained earnings	3,662,773
Accounting Standards Update 2014-09 [Member] | Effect of Change Higher/(Lower) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net revenues	(10,132)
Total cost of net revenues	160
Gross margin	(10,292)
Total operating expenses	(3,341)
Income from operations	(6,951)
Net income	$ (6,643)
Basic earnings per share (in dollars per share)	$ (0.04)
Diluted earnings per share (in dollars per share)	$ (0.04)
Contract assets	$ 7,307			$ 7,300
Contract acquisition costs	69,573
Deferred tax assets, net	(29,860)
Total assets	47,020
Deferred tax liabilities	13,079
Current portion of deferred revenues	(51,109)
Long-term portion of deferred revenues	(38,698)
Total liabilities	(76,728)
Retained earnings	$ 123,748			$ 130,700

[1] As noted above, prior period amounts have not been adjusted under the modified retrospective method. See Note 2 for further information regarding the Company’s adoption of the revenue recognition standard.