Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Oct. 31, 2019	Oct. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 90,770	$ 79,250	$ 55,400	$ 114,216	$ 75,866	$ 33,699	$ 225,420	$ 223,781
Weighted average common shares - basic	35,720,000			38,358,000			36,395,000	38,357,000
Equity based awards	248,000			168,000			235,000	202,000
Weighted average common shares - diluted	35,968,000			38,526,000			36,630,000	38,559,000
Basic Earnings Per Share	$ 2.54			$ 2.98			$ 6.19	$ 5.83
Diluted Earnings Per Share	$ 2.52			$ 2.96			$ 6.15	$ 5.80
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	485			45,072			485	43,783