Restructuring Expenses - Components of Restructuring Expenses (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	$ 5,058	$ 0		$ 0
Restructuring charges	0	7,420	$ 0	7,420	$ 0
Payments	(3,281)	(2,362)
Accrued restructuring, end of period	1,777	5,058		1,777
Workforce reduction
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	4,875	0		0
Restructuring charges		7,034
Payments	(3,098)	(2,159)
Accrued restructuring, end of period	1,777	4,875		1,777
Contract termination
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	170	0		0
Restructuring charges		229
Payments	(170)	(59)
Accrued restructuring, end of period	0	170		0
Other
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning of period	13	0		0
Restructuring charges		157
Payments	(13)	(144)
Accrued restructuring, end of period	$ 0	$ 13		$ 0