Derivative Instruments and Hedging Activities (Details)	3 Months Ended		6 Months Ended
	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2012 Other Assets Foreign Exchange Forward USD ($)	Sep. 30, 2012 Accounts Payable and Accrued Liabilities Foreign Exchange Forward USD ($)	Sep. 30, 2012 Sell British Pounds in Exchange for US Dollars United Kingdom, Pounds Foreign Exchange Forward USD ($)	Sep. 30, 2012 Sell British Pounds in Exchange for US Dollars United Kingdom, Pounds Foreign Exchange Forward GBP (£)	Sep. 30, 2012 Purchase British Pounds in Exchange for US Dollars United Kingdom, Pounds Foreign Exchange Forward USD ($)	Sep. 30, 2012 Purchase British Pounds in Exchange for US Dollars United Kingdom, Pounds Foreign Exchange Forward GBP (£)	Sep. 30, 2012 Purchase Canadian Dollars in Exchange for US Dollars Canada, Dollars Foreign Exchange Forward USD ($)	Sep. 30, 2012 Purchase Canadian Dollars in Exchange for US Dollars Canada, Dollars Foreign Exchange Forward CAD	Sep. 30, 2012 Purchase Euros in Exchange for US Dollars Euro Member Countries, Euro Foreign Exchange Forward USD ($)	Sep. 30, 2012 Purchase Euros in Exchange for US Dollars Euro Member Countries, Euro Foreign Exchange Forward EUR (€)
Derivative [Line Items]
Notional amount of foreign currency derivative sale contracts								£ 7,900,000
Derivative, average forward exchange rate							1.60		1.59		1.00		1.27
Notional amount of foreign currency derivative purchase contracts							12,700,000		28,500,000.0	18,000,000	7,800,000	7,800,000	4,100,000	3,200,000
Remaining maturity of foreign currency derivatives, maximum							7 months	7 months	3 months	3 months	5 months	5 months	1 month	1 month
Net unrealized gain (loss) on foreign exchange contracts	(512,000)	626,000	(17,000)	662,000
Gain on cash flow hedge ineffectiveness	600,000	0	600,000	0
Derivative assets					600,000
Derivative liabilities						$ 200,000