Stockholders' Investment (Tables)

9 Months Ended

Sep. 30, 2013

Equity [Abstract]

Schedule of changes in stockholders' investment

	Three Months Ended September 30,					Nine Months Ended September 30,
	2013		2012			2013		2012
Beginning balance	$	429,973	$	315,524		$	392,079	$	295,953
Net income	13,230		9,872			37,782		28,003
Shared-based compensation	451		174			1,155		493
Issuance of common stock - stock offering	38,150		—			46,653		—
Issuance of common stock - options and warrants	2,176		1,203			6,311		2,060
Excess tax benefit on stock-based compensation	3,765		—			3,765		—
Other Changes	—		(1,501		)	—		(1,237		)
Ending balance	$	487,745	$	325,272		$	487,745	$	325,272