Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 114,216	$ 37,268	$ 223,781	$ 115,381
Weighted average common shares - basic	38,358,000	38,186,000	38,357,000	37,877,000
Equity based awards	168,000	247,000	202,000	228,000
Weighted average common shares - diluted	38,526,000	38,433,000	38,559,000	38,105,000
Basic Earnings Per Share	$ 2.98	$ 0.98	$ 5.83	$ 3.05
Diluted Earnings Per Share	$ 2.96	$ 0.97	$ 5.80	$ 3.03
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	45,072	15,739	43,783	30,578