Income Taxes - Summary of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2016	Jul. 31, 2015
Income Tax Disclosure [Abstract]
Income before income taxes	$ 9,433	$ 25,048	$ 10,808	$ 45,400
Provision for income taxes	$ 801	$ 1,951	$ 393	$ 3,449
Effective tax rate	8.50%	7.80%	3.60%	7.60%