Income Taxes - Summary of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Income Tax Disclosure [Abstract]
Income before income taxes	$ 29,802	$ 30,496	$ 40,610	$ 75,896
Provision for income taxes	$ 757	$ 1,035	$ 1,150	$ 4,484
Effective tax rate	2.50%	3.40%	2.80%	5.90%