Segment Reporting - Additional Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Concentration Risk
Total revenues	$ 439,066	$ 292,683	$ 260,233	$ 252,151	$ 401,000	$ 275,642	$ 253,216	$ 226,515	$ 1,244,133	$ 1,156,373	$ 1,088,727
Customers accounting for ten percent or more of net revenue									0	0	0
Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Concentration Risk
Customer percent of total revenues									10.00%	10.00%	10.00%
KOREA, REPUBLIC OF
Concentration Risk
Total revenues									$ 135,696
Customer percent of total revenues									10.90%