Changes in Stockholders' Equity and Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Changes In Stockholders Equity and Comprehensive Income [Line Items]
Beginning balance at March 31, 2012:			$ 81,181
Net income	4,034	3,930	7,986	8,767
Net change in unrealized gain on short term investments	16	22	25	68
Ending balance at September 30, 2012:	80,113		80,113
Additional Paid-In Capital
Changes In Stockholders Equity and Comprehensive Income [Line Items]
Beginning balance at March 31, 2012:
Share based compensation			1,039
Dividends declared
Net income
Repurchased and retired shares			(3,865)
Deferred tax adjustment related to resticted stock			(168)
Allocation of retirement of additional paid in capital and and retained earnings			2,994
Net change in unrealized gain on short term investments
Ending balance at September 30, 2012:
Retained Earnings
Changes In Stockholders Equity and Comprehensive Income [Line Items]
Beginning balance at March 31, 2012:			81,108
Share based compensation
Dividends declared			(6,085)
Net income			7,986
Repurchased and retired shares
Deferred tax adjustment related to resticted stock
Allocation of retirement of additional paid in capital and and retained earnings			(2,994)
Net change in unrealized gain on short term investments
Ending balance at September 30, 2012:	80,015		80,015
Accumulated Other Comprehensive Gain
Changes In Stockholders Equity and Comprehensive Income [Line Items]
Beginning balance at March 31, 2012:			44
Share based compensation
Dividends declared
Net income
Repurchased and retired shares
Deferred tax adjustment related to resticted stock
Allocation of retirement of additional paid in capital and and retained earnings
Net change in unrealized gain on short term investments			25
Ending balance at September 30, 2012:	$ 69		$ 69