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Share-Based Compensation - Summarized Information of Stock Options Outstanding (Details) - Stock Options
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
$ / shares
shares
Outstanding:  
Aggregate intrinsic value $ 55,789
Weighted average remaining contractual life 6 years 6 months
Exercisable:  
Number of options (in shares) | shares 954
Weighted average exercise price (in dollars per share) | $ / shares $ 22.19
Aggregate intrinsic value $ 29,134
Weighted average remaining contractual life 4 years 8 months 12 days