Description of Business and Summary of Significant Accounting Policies - Narrative (Details) - USD ($)			1 Months Ended	3 Months Ended
	Feb. 01, 2016	Jan. 14, 2016	Jun. 30, 2015	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Business Acquisition [Line Items]
Liabilities incurred				$ 35,588,000	$ 0
Consideration transferred, equity interests				39,300,000	$ 0
Debt Instrument [Line Items]
Stock repurchased during period			$ 150,000,000
Stock repurchase during period (shares)			3,300,000
New Accounting Pronouncement, Early Adoption [Line Items]
Income tax deficiencies, less than				$ 100,000
Convertible Senior Notes
Debt Instrument [Line Items]
Net proceeds from issuance of convertible senior notes			$ 896,500,000
Invotas International Corporation
Business Acquisition [Line Items]
Purchase consideration, cash paid	$ 17,700,000
iSIGHT Security
Business Acquisition [Line Items]
Purchase consideration, cash paid		$ 192,800,000
Liabilities incurred		$ 35,600,000
Common Stock | Invotas International Corporation
Business Acquisition [Line Items]
Equity interest issuable, number of shares	742,026
Consideration transferred, equity interests	$ 11,100,000
Common Stock | iSIGHT Security
Business Acquisition [Line Items]
Equity interest issuable, number of shares		1,793,305
Consideration transferred, equity interests		$ 28,200,000
Series A Notes | Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount			$ 460,000,000
Interest rate			1.00%
Series B Notes | Convertible Senior Notes
Debt Instrument [Line Items]
Principal amount			$ 460,000,000
Interest rate			1.625%
Accounting Standards Update 2016-09 | New Accounting Pronouncement, Early Adoption, Effect | Retained Earnings
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative-effect adjustment to retained earnings						$ 3,400,000