Earnings Per Share ("EPS") (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended											12 Months Ended
	Jan. 31, 2019		Oct. 31, 2018		Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018		Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Earnings Per Share (EPS) [Abstract]
Net income	$ 116,799	[1]	$ 114,216	[1]	$ 75,866	$ 33,699	$ 1,260	[2]	$ 37,268	$ 47,459	$ 30,654	$ 340,580	$ 116,641	$ 195,095
Weighted average common shares - basic												38,094,000	37,957,000	35,194,000
Equity-based awards												223,000	259,000	234,000
Weighted average common shares - diluted												38,317,000	38,216,000	35,428,000
Basic	$ 3.13		$ 2.98		$ 1.97	$ 0.88	$ 0.03		$ 0.98	$ 1.24	$ 0.82	$ 8.94	$ 3.07	$ 5.54
Diluted	$ 3.11		$ 2.96		$ 1.97	$ 0.87	$ 0.03		$ 0.97	$ 1.24	$ 0.82	$ 8.89	$ 3.05	$ 5.51
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount												21,008	3,017	5,191

[1] The Company decreased its estimate of the one-time transition tax related to the enactment of U.S. Tax Reform by $24.0 million and $25.2 million, respectively, in the third and fourth quarters of fiscal 2019 (see Note 9 – Income Taxes for further discussion).

[2] The Company recorded income tax expenses of $95.4 million in the fourth quarter of fiscal 2018 related to the impact of the enactment of U.S. Tax Reform.