Summary of Significant Accounting Policies (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Weighted-average shares outstanding for basic and diluted net income per share
Net income	$ 5,201	$ (12,587)	$ 10,121	$ 12,945	$ (4,090)	$ 15,626	$ 15,691	$ 15,497	$ 15,680	$ 42,724	$ 75,657
Basic net income per share:
Weighted-average shares outstanding - Basic	60,208	60,173	59,734	59,559	59,541	59,400	59,347	59,281	59,918	59,392	58,729
Basic net income per common share	$ 0.09	$ (0.21)	$ 0.17	$ 0.22	$ (0.07)	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.72	$ 1.29
Diluted net income per share:
Weighted-average shares outstanding - Basic	60,208	60,173	59,734	59,559	59,541	59,400	59,347	59,281	59,918	59,392	58,729
Effect of potentially dilutive securities									216	70	320
Weighted-average shares outstanding - Diluted	60,592	60,173	59,751	59,572	59,541	59,405	59,386	59,388	60,134	59,462	59,049
Diluted net income per common share	$ 0.09	$ (0.21)	$ 0.17	$ 0.22	$ (0.07)	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.72	$ 1.28