Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator
Net income	$ 16,533	$ 16,279	$ 30,344	$ 35,881
Denominator
Basic weighted-average shares outstanding	60,573	60,058	60,558	59,918
Dilutive effect of restricted stock units and stock options	458	319	423	310
Diluted weighted-average shares outstanding	61,031	60,377	60,981	60,228
Per share income
Basic (in dollars per share)	$ 0.27	$ 0.27	$ 0.50	$ 0.60
Diluted income per share: (in dollars per share)	$ 0.27	$ 0.27	$ 0.50	$ 0.59
Basic weighted-average shares outstanding (in shares)	60,573	60,058	60,558	59,918