Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Statement of Comprehensive Income [Abstract]
Unrealized gains on cash equivalents, marketable securities and restricted investment, taxes	$ 0	$ 73	$ 810
Changes in market value of derivatives, taxes (benefit)	33	(146)	(129)
Reclassification adjustment for net gains included in net income, taxes	$ 62	$ 91	$ 78