Industry Segment and Geographic Areas (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from External Customers and Long-Lived Assets
Revenues:	$ 81,010	$ 92,963	$ 88,341	$ 71,808	$ 74,323	$ 87,130	$ 81,974	$ 76,233	$ 334,122	$ 319,660	$ 262,915
Long-lived assets (all non-current assets):	188,895				169,079				188,895	169,079
Total assets:	316,058				290,453				316,058	290,453
United States
Revenues from External Customers and Long-Lived Assets
Revenues:									290,019	271,045	231,306
Long-lived assets (all non-current assets):	150,997				133,628				150,997	133,628
Total assets:	255,881				236,442				255,881	236,442
Asia
Revenues from External Customers and Long-Lived Assets
Revenues:									8,085	10,075	2,229
Canada
Revenues from External Customers and Long-Lived Assets
Revenues:									8,514	8,752	3,362
Europe
Revenues from External Customers and Long-Lived Assets
Revenues:									15,677	16,001	12,997
Long-lived assets (all non-current assets):	17,409				15,261				17,409	15,261
Total assets:	36,838				31,461				36,838	31,461
Mexico
Revenues from External Customers and Long-Lived Assets
Revenues:									4,226	6,636	8,178
Long-lived assets (all non-current assets):	20,489				20,190				20,489	20,190
Total assets:	23,339				22,550				23,339	22,550
Other
Revenues from External Customers and Long-Lived Assets
Revenues:									$ 7,601	$ 7,151	$ 4,843