Restructuring and Impairment Charges - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Arizona
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 400	$ 700
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	53
Expected cost to be paid	1,100
Cost expensed	$ 100