Segment Reporting - Company's Revenue by Geographic Region (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Revenue from External Customer [Line Items]
Total revenue	$ 310,297	$ 316,373	$ 218,278
Hong Kong [Member]
Revenue from External Customer [Line Items]
Total revenue	276,972	284,722	196,372
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	13,119	8,913	6,795
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	7,038	8,855	6,677
North America other than United States [Member]
Revenue from External Customer [Line Items]
Total revenue	3,687	9,953	6,076
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	$ 9,481	$ 3,930	$ 2,358