Stock-Based Compensation - Stock Award Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock option activity
Total options outstanding, end of period (in shares)	5,490,626
Weighted-Average Exercise Price
Total options outstanding at the end of the period (in dollars per share)	$ 42.81
Stock options
Stock option activity
Total options outstanding, beginning of period (in shares)	7,923,009	6,845,685	11,725,823
Granted (in shares)	3,468,626	1,901,000	452,000
Exercised (in shares)	(514,401)	(431,092)	(1,884,938)
Forfeited and cancelled (in shares)	(2,029,500)	(392,584)	(3,447,200)
Total options outstanding, end of period (in shares)	8,847,734	7,923,009	6,845,685
Exercisable at the end of the period (in shares)	1,772,608	1,892,809	1,965,585
Weighted-Average Exercise Price
Total options outstanding, beginning of the period (in dollars per share)	$ 36.21	$ 31.13	$ 24.51
Granted (in dollars per share)	59.66	54.41	69.11
Exercised (in dollars per share)	28.70	23.36	16.15
Forfeited and cancelled (in dollars per share)	44.64	50.03	21.78
Total options outstanding at the end of the period (in dollars per share)	43.90	36.21	31.13
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 35.13	$ 29.97	$ 26.82
Share-based compensation additional disclosures
Tax benefit from stock awards exercised	$ 9,347	$ 5,006	$ 33,716
Additional disclosures
Aggregate intrinsic value of stock options outstanding	88,990
Aggregate intrinsic value of stock options exercisable	$ 28,175
Stock options | Long-Term Performance Based Plans
Stock option activity
Total options outstanding, beginning of period (in shares)	4,312,000	3,904,500
Total options outstanding, end of period (in shares)	5,490,626	4,312,000	3,904,500
Weighted-Average Exercise Price
Total options outstanding, beginning of the period (in dollars per share)	$ 31.39	$ 28.03
Total options outstanding at the end of the period (in dollars per share)	$ 42.81	$ 31.39	$ 28.03