Share-Based Compensation - Stock Option Activity (Details) - Stock Options	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Non-Vested Stock Options Outstanding, Number of Options
Beginning balance (in shares) | shares	330,870
Vested (in shares) | shares	(77,388)
Ending balance (in shares) | shares	253,482
Non-Vested Stock Options Outstanding, Weighted- Average Grant Date Fair Value Per Share
Beginning balance (dollars per share)	$ 7.09
Vested (dollars per share)	6.93
Ending balance (dollars per share)	$ 7.14
Stock Options Outstanding, Number of Options
Beginning balance (in shares) | shares	1,110,918
Exercised (in shares) | shares	(186,434)
Ending balance (in shares) | shares	924,484
Weighted- Average Exercise Price Per Share
Beginning balance, Weighted Average Exercise Price (dollars per share)	$ 29.56
Exercised, Weighted Average Exercise Price (dollars per share)	20.24
Ending balance, Weighted Average Exercise Price (dollars per share)	$ 31.44
Exercisable/vested, Number of Options (in shares) | shares	671,002
Exercisable/vested, Weighted Average Exercise Price (dollars per share)	$ 28.86
Non Vested
Weighted- Average Exercise Price Per Share
Beginning balance, Weighted Average Exercise Price (dollars per share)	37.97
Vested, Weighted Average Exercise Price (dollars per share)	37.01
Ending balance, Weighted Average Exercise Price (dollars per share)	$ 38.26