SIGNIFICANT ACCOUNTING POLICIES - Reconciliation between Basic and Diluted Net Income per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Accounting Policies [Abstract]
Net income	$ 25,288	$ 95,387	$ 11,119	$ 12,043	$ 24,080	$ 94,025	$ 10,077	$ 9,885	$ 143,837	$ 138,067	$ 62,124
Basic net income per share:
Basic common shares									48,209	49,140	48,820
Basic net income per share (in dollars per share)	$ 0.53	$ 2.00	$ 0.23	$ 0.25	$ 0.49	$ 1.91	$ 0.20	$ 0.20	$ 2.98	$ 2.81	$ 1.27
Diluted net income per share:
Basic common shares									48,209	49,140	48,820
Diluted restricted stock awards and stock options									686	1,134	930
Diluted common shares									48,895	50,274	49,750
Diluted net income per share (in dollars per share)	$ 0.52	$ 1.97	$ 0.23	$ 0.24	$ 0.48	$ 1.86	$ 0.20	$ 0.20	$ 2.94	$ 2.75	$ 1.25