Stockholders' Investment (Tables)

6 Months Ended

Jun. 30, 2016

Equity [Abstract]

Schedule of changes in stockholders' investment

	Three Months Ended					Six Months Ended
	June 30,					June 30,
	2016			2015		2016			2015
Beginning balance	$	616,504		$	575,325	$	613,307		$	558,775
Net income	1,798			16,471		4,863			30,075
Share-based compensation	577			825		1,126			1,621
Issuance of common stock from share-based compensation	—			1,811		—			3,150
Excess tax benefit on share-based compensation	—			380		—			1,191
Other changes	(45		)	—		(462		)	—
Ending balance	$	618,834		$	594,812	$	618,834		$	594,812