Segment Information - Revenues and Long-Lived Assets by Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 184,585	$ 170,150	$ 188,213	$ 187,557	$ 170,291	$ 164,619	$ 188,735	$ 196,355	$ 730,505	$ 720,000	$ 745,770
Long-lived assets	343,112				356,362				343,112	356,362
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									626,805	606,134	634,076
Long-lived assets	326,591				334,541				326,591	334,541
Mexico
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									94,905	100,689	98,128
Long-lived assets	15,893				20,995				15,893	20,995
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									8,795	13,177	$ 13,566
Long-lived assets	$ 628				$ 826				$ 628	$ 826