Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator
Net income	$ 21,200	$ 15,552	$ 51,544	$ 51,432
Denominator
Basic weighted-average shares outstanding	60,760	60,328	60,626	60,056
Dilutive effect of restricted stock units and stock options	260	202	372	281
Diluted weighted-average shares outstanding	61,020	60,530	60,998	60,337
Per share income
Basic (in dollars per share)	$ 0.35	$ 0.26	$ 0.85	$ 0.85
Diluted income per share: (in dollars per share)	$ 0.35	$ 0.26	$ 0.85	$ 0.85
Basic weighted-average shares outstanding (in shares)	60,760	60,328	60,626	60,056