Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Numerator
Income from continuing operations									$ 65,505	$ 37,212	$ 29,179
Income from discontinued operations and loss on sale of discontinued operations									0	0	41
Net income	$ 19,349	$ 12,257	$ 19,244	$ 14,655	$ (15)	$ 9,510	$ 12,949	$ 14,768	$ 65,505	$ 37,212	$ 29,220
Denominator
Denominator for basic earnings per share- weighted average shares (in shares)	51,147	50,686	50,364	50,342	50,314	50,307	50,278	50,183	50,633	50,270	50,081
Dilutive effect of unvested restricted common stock (including restricted stock units) and options issued to employees and directors (in shares)									807	478	257
Denominator for diluted earnings per share (in shares)	51,913	51,523	51,225	51,106	50,992	50,684	50,671	50,646	51,440	50,748	50,338
Earnings per Common Share:
Basic earnings per share from continuing operations (in USD per share)									$ 1.29	$ 0.74	$ 0.58
Basic earnings per share from discontinued operations and loss on sale of discontinued operations (in USD per share)									$ 0.00	$ 0.00	$ 0.00
Basic net earnings per share (in USD per share)	$ 0.38	$ 0.24	$ 0.38	$ 0.29	$ 0.00	$ 0.19	$ 0.26	$ 0.29	$ 1.29	$ 0.74	$ 0.58
Diluted earnings per share from continuing operations (in USD per share)									$ 1.27	$ 0.73	$ 0.58
Diluted earnings per share from discontinued operations and loss on sale of discontinued operations (in USD per share)									$ 0.00	$ 0.00	$ 0.00
Diluted net earnings per share (in USD per share)	$ 0.37	$ 0.24	$ 0.38	$ 0.29	$ 0.00	$ 0.19	$ 0.26	$ 0.29	$ 1.27	$ 0.73	$ 0.58