Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 37,268	$ 36,506	$ 115,381	$ 116,273
Weighted average common shares - basic	38,186,000	35,218,000	37,877,000	35,184,000
Equity based awards	247,000	231,000	228,000	209,000
Weighted average common shares - diluted	38,433,000	35,449,000	38,105,000	35,393,000
Basic EPS	$ 0.98	$ 1.04	$ 3.05	$ 3.30
Diluted EPS	$ 0.97	$ 1.03	$ 3.03	$ 3.29
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	15,739	844	30,578	1,454