Debt - Schedule of Interest Expense (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
Debt Disclosure [Abstract]
Contractual interest expense	$ 2,190	$ 3,329	$ 7,777	$ 6,922
Amortization of debt issuance costs	1,132	1,275	3,490	3,195
Amortization of debt discount	8,637	12,547	28,837	34,139
Debt Instrument, Interest Expense, Total	$ 11,959	$ 17,151	$ 40,104	$ 44,256