Shareholders' Equity - Schedule of Grant Date Fair Value and Stock-based Compensation Expense Allocated (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 4,463	$ 9,815	$ 22,324
Stock Options
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Weighted average, grant date fair value	$ 8.54	$ 6.91	$ 3.81
Restricted Shares (RSAs and RSUs)
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Weighted average, grant date fair value	$ 31.90	$ 15.08	$ 12.53
Direct Costs, Excluding Depreciation and Amortization
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,128	$ 5,555	$ 9,243
Selling, General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,335	$ 4,260	$ 13,081