Share-Based Compensation - Narrative (Details) - USD ($)	1 Months Ended				3 Months Ended		6 Months Ended
	Mar. 31, 2018	Feb. 28, 2018	Mar. 31, 2017	Feb. 28, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Repurchase of common stock for employee tax withholding obligations amount, shares							19,237	25,642
Repurchase of common stock for employee tax withholding obligations amount							$ 1,000,000	$ 1,200,000
2017 Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Useful Life of the plan							10 years
Common stock shares issuable						1,750,000		1,750,000
Shares available for grant					1,667,216		1,667,216
2007 Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Award vesting period							3 years
2007 Plan | Performance Unit Incentive Plan (“PUP”)
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Awards with grant date fair value during the period							$ 4,000,000
Stock value payable							1,600,000
Liability awards recorded					$ 6,000,000		6,000,000		$ 11,000,000
Payments to employees	$ 5,900,000		$ 3,700,000
2007 Plan | Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Unamortized cost					3,700,000		$ 3,700,000
Recognition period of unrecognized cost							1 year 4 months 24 days
Repurchase of common stock for employee tax withholding obligations amount, shares							19,237	25,642
Repurchase of common stock for employee tax withholding obligations amount							$ 1,000,000	$ 1,200,000
2007 Plan | Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Payments to employees		$ 200,000		$ 300,000
Liabilities related to restricted stock					300,000		300,000		$ 500,000
Restructuring Charges
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation before income tax benefit					$ 0	$ 0	$ 0	$ 0