Stockholders' Equity, Stock Option Activity (Details) - Stock Options [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares [Abstract]
Outstanding at beginning of period (in shares)	9,178
Granted (in shares)	3,274
Exercised (in shares)	(1,345)
Cancelled/forfeited/expired (in shares)	(1,710)
Outstanding at end of period (in shares)	9,397	9,178
Exercisable at end of period (in shares)	5,182
Weighted Average Exercise Price Per Share [Abstract]
Outstanding at beginning of period (in dollars per share)	$ 40.48
Granted (in dollars per share)	47.76
Exercised (in dollars per share)	15.74
Cancelled/forfeited/expired (in dollars per share)	51.71
Outstanding at end of period (in dollars per share)	44.52	$ 40.48
Exercisable at end of period (in dollars per share)	$ 39.10
Average Remaining Contractual Term, Aggregate Intrinsic Value and Other [Abstract]
Average remaining contractual term, outstanding at end of period	4 years 5 months 1 day
Average remaining contractual term, exercisable at end of period	3 years 3 months 29 days
Aggregate intrinsic value, outstanding at end of period	$ 92,288
Aggregate intrinsic value, exercisable at end of period	$ 80,167
Weighted average fair value of options granted (in dollars per share)	$ 25.42	$ 26.72	$ 27.44
Intrinsic value of options exercised	$ 49,500	$ 28,000	$ 84,700
Cash received from exercise of stock options	$ 21,200	$ 12,600	$ 23,600
Weighted-average fair value of options exercised (in dollars per share)	$ 52.53
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation expense related to non-vested stock options	$ 75,200
Weighted average period for recognition	1 year 2 months 12 days