Share-Based Payments - Summary of Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation	$ 21,222	$ 16,127	$ 18,322
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation	7,081	10,036	9,831
Restricted stock awards and restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation	10,032	5,608	8,064
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation	301	483	427
Awards Relating To Restructuring [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation	$ 3,808	$ 0	$ 0