Significant Accounting Policies (Net Income 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
Significant Accounting Policies Net Income Per Share Details
Net income available to common stockholders	$ 1,661	$ 1,920	$ 1,741	$ 8,617	$ 63,863	$ 2,586	$ 832	$ 1,947	$ 13,939	$ 69,228	$ 6,494
Common shares	71,998	71,611	71,261	70,717	70,205	69,445	63,710	62,264	71,390	66,413	63,087
Denominator for basic calculation	71,998	71,611	71,261	70,717	70,205	69,445	63,710	62,264	71,390	66,413	63,087
Employee stock options									2,958	3,327	2,564
Employee restricted purchase rights									352	409	222
Denominator for diluted calculation	75,053	74,988	74,558	74,110	73,648	73,214	67,759	65,808	74,700	70,149	65,873
Net income per share
Basic	$ 0.02	$ 0.03	$ 0.02	$ 0.12	$ 0.91	$ 0.04	$ 0.01	$ 0.03	$ 0.20	$ 1.04	$ 0.10
Diluted	$ 0.02	$ 0.03	$ 0.02	$ 0.12	$ 0.87	$ 0.04	$ 0.01	$ 0.03	$ 0.19	$ 0.99	$ 0.10