Workforce Reduction - Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Workforce Reduction
Charges	$ 2,392	$ 4,814
Employee severance, benefits and related costs
Workforce Reduction
Balance at beginning of period	1,160
Charges	2,166
Amounts Paid	(1,016)
Balance at end of period	2,310	2,310
Employee severance, benefits and related costs | Reduction in Field-based Workforce, January 30, 2018
Workforce Reduction
Balance at beginning of period	1,160
Amounts Paid	(1,016)
Balance at end of period	144	144
Employee severance, benefits and related costs | Reduction in Headquarter-based Workforce, June 27, 2018
Workforce Reduction
Balance at beginning of period	0
Charges	2,166
Balance at end of period	$ 2,166	$ 2,166