Stock-Based Compensation - Summary of Exercisable Options and Appreciation Rights (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Exercised Units | shares	93,920
Weighted Average Exercised Price (in dollars per share) | $ / shares	$ 1.81
Number of Exercisable Units | shares	397,651
Weighted Average Exercisable Price (in dollars per share) | $ / shares	$ 14.39
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Exercised Units | shares	0
Weighted Average Exercised Price (in dollars per share) | $ / shares	$ 0.00
Number of Exercisable Units | shares	42,152
Weighted Average Exercisable Price (in dollars per share) | $ / shares	$ 14.14