Investments - Schedule of Components of Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Interest income	$ 2,720	$ 1,258	$ 7,051	$ 8,029
Realized gains	78	332	424	5,732
Realized losses	(176)	(480)	(420)	(4,910)
Total investment income	$ 2,622	$ 1,110	$ 7,055	$ 8,851