CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 9,604	$ 10,601
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,613	2,535
Provisions for contracts, inventory and accounts receivable reserves	1,543	1,223
Amortization of bond premium	855	1,486
Stock compensation expense (credit)	641	(104)
Deferred income taxes	1,894
Changes in assets and liabilities:
Accounts receivable	7,490	(2,404)
Unbilled costs and fees	5	366
Inventories	(4,332)	(226)
Prepaid expenses and other assets	1,640	613
Accounts payable	2,873	(897)
Accrued income taxes	(2,094)	991
Customer deposits	12,731	6,309
Deferred revenue	(3,077)	(3,934)
Accrued expenses and other liabilities	(3,756)	(1,234)
Net cash provided by operating activities	28,630	15,325
Cash flows from investing activities:
Purchases of short-term investments	(18,311)	(53,362)
Proceeds from sales and maturities of short-term investments	57,534	96,540
Purchases of property and equipment, net	(1,249)	(2,007)
Net cash provided by investing activities	37,974	41,171
Cash flows from financing activities:
Increase in restricted cash and investments	(1,222)	(1,348)
Proceeds from exercise of stock options	1,497	282
Repurchase of shares of common stock	(12,306)	(34,967)
Repayment of leasehold financing liability	(742)	(667)
Payment of common stock dividend	(7,800)	(8,621)
Reduction of income taxes paid due to the tax benefit from employee stock option expense	20
Net cash used for financing activities	(20,553)	(45,321)
Net increase in cash and cash equivalents	46,051	11,175
Cash and cash equivalents at beginning of period	40,418	24,369
Cash and cash equivalents at end of period	$ 86,469	$ 35,544