Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 75,866	$ 47,459	$ 109,565	$ 78,113
Weighted average common shares - basic	38,428,000	38,174,000	38,356,000	37,720,000
Equity based awards	138,000	214,000	209,000	215,000
Weighted average common shares - diluted	38,566,000	38,388,000	38,565,000	37,935,000
Basic Earnings Per Share	$ 1.97	$ 1.24	$ 2.86	$ 2.07
Diluted Earnings Per Share	$ 1.97	$ 1.24	$ 2.84	$ 2.06
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	46,727	26,454	46,212	36,956