Restructuring Activities - Charges and Net Assets (Details) - USD ($) $ in Thousands		3 Months Ended						9 Months Ended
	Jan. 23, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Total Revenues		$ 6,452			$ 16,070			$ 25,555	$ 40,708
Net income (loss)		(1,278)	$ (945)	$ (1,289)	1,045	$ (1,753)	$ (216)	(3,512)	(924)
Total assets		37,879						37,879		$ 51,719
Liabilities		(7,238)						(7,238)		(17,667)
Payments for restructuring		155			93			690	296
Restructuring charge		0			0			625	0
CHINA
Restructuring Cost and Reserve [Line Items]
Remaining performance requirements for APC projects		47						47
Total Revenues		0			1,066			311	2,406
Net income (loss)		(80)			$ (435)			(1,469)	$ (1,588)
Total assets		4,308						4,308		8,546
Liabilities		(266)						(266)		(2,953)
Total net assets		4,042						4,042		$ 5,593
CHINA | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring, expected cost		562						562
Payments for restructuring		$ 90						562
Restructuring charge								562
CHINA | Facility Closing
Restructuring Cost and Reserve [Line Items]
Restructuring charge	$ 63							$ 63