Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 11,724	$ 29,045	$ 17,591	$ 39,460
Other comprehensive loss, net of tax:
Unrealized losses on investments	(34)	(51)	(46)	(11)
Other comprehensive loss, net of tax	(34)	(51)	(46)	(11)
Comprehensive income	$ 11,690	$ 28,994	$ 17,545	$ 39,449

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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