Restructuring Expenses - Components of Restructuring Expenses (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	$ 1,777			$ 0	$ 0
Restructuring charges	0		$ 0	7,420	7,420	$ 0
Payments		$ (579)		(5,643)
Accrued restructuring, end of period	1,198	1,777		1,777	1,198
Workforce reduction
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	1,777			0	0
Restructuring charges				7,034
Payments		(579)		(5,257)
Accrued restructuring, end of period	1,198	1,777		1,777	1,198
Contract termination
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	0			0	0
Restructuring charges				229
Payments		0		(229)
Accrued restructuring, end of period	0	0		0	0
Other
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	0			0	0
Restructuring charges				157
Payments		0		(157)
Accrued restructuring, end of period	$ 0	$ 0		$ 0	$ 0