Stock-Based Compensation - Valuation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-Based Compensation
Non-cash stock-based compensation expense recognized	$ 13,037	$ 19,199	$ 34,153
Stock options
Black-Scholes option valuation model, assumptions
Risk free interest rate, low end of range (as a percent)	1.06%	1.40%	1.80%
Risk free interest rate, high end of range (as a percent)	2.27%	2.19%	2.84%
Volatility factor, low end of range (as a percent)	26.12%	26.42%	28.53%
Volatility factor, high end of range (as a percent)	33.37%	36.22%	38.62%
Stock options | Minimum
Black-Scholes option valuation model, assumptions
Expected term of options	5 years 4 months 24 days	5 years 6 months	5 years 6 months
Weighted-average fair value of options granted (in dollars per share)	$ 12.45	$ 16.14	$ 19.08
Stock options | Maximum
Black-Scholes option valuation model, assumptions
Expected term of options	10 years	7 years 9 months 18 days	9 years
Weighted-average fair value of options granted (in dollars per share)	$ 26.86	$ 29.73	$ 29.20