Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Apr. 30, 2018	Jul. 31, 2019	Jul. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 79,250	$ 55,400	$ 75,866	$ 33,699	$ 134,650	$ 109,565
Weighted average common shares - basic	36,476,000		38,428,000		36,739,000	38,356,000
Equity based awards	185,000		138,000		225,000	209,000
Weighted average common shares - diluted	36,661,000		38,566,000		36,964,000	38,565,000
Basic Earnings Per Share	$ 2.17		$ 1.97		$ 3.67	$ 2.86
Diluted Earnings Per Share	$ 2.16		$ 1.97		$ 3.64	$ 2.84
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	692		46,727		692	46,212