Share-Based Compensation - Summary of Stock Options Activity (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of Shares
Beginning of period (in shares) | shares	2,615
Granted (in shares) | shares	544
Exercised (in shares) | shares	(682)
Forfeited (in shares) | shares	(100)
Expired (in shares) | shares	(3)
End of period (in shares) | shares	2,374
Weighted Average Exercise Price
Beginning of period (in dollars per share) | $ / shares	$ 24.61
Granted (in dollars per share) | $ / shares	39.38
Exercised (in dollars per share) | $ / shares	18.95
Forfeited (in dollars per share) | $ / shares	34.10
Expired (in dollars per share) | $ / shares	23.49
End of period (in dollars per share) | $ / shares	$ 29.22