Share Incentive Plans - Information Regarding Options Outstanding and Exercisable (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share Based Compensation [Abstract]
Options Outstanding, Options | shares	6,483,832
Options Exercisable, Options | shares	5,336,043
Options, Vested and expected to vest | shares	6,413,817
Options Outstanding, Weighted Average Remaining Contractual Life in Years	4 years 11 months 15 days
Options Exercisable, Weighted Average Remaining Contractual Life in Years	4 years 1 month 6 days
Options, Weighted Average Remaining Contractual Life in Years	2 years 9 months 18 days
Options Outstanding, Weighted Average Exercise Price | $ / shares	$ 46.06
Options Exercisable, Weighted Average Exercise Price | $ / shares	43.24
Vested and expected to vest, Weighted Average Exercise Price | $ / shares	$ 34.39
Options Outstanding, Aggregate Intrinsic Value | $	$ 113,379
Options Exercisable, Aggregate Intrinsic Value | $	110,332
Vested and expected to vest, Aggregate Intrinsic Value | $	$ 113,201