Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 47,459	$ 46,394	$ 78,113	$ 79,767
Weighted average common shares - basic	38,174,000	35,207,000	37,720,000	35,167,000
Equity based awards	214,000	171,000	215,000	206,000
Weighted average common shares - diluted	38,388,000	35,378,000	37,935,000	35,373,000
Basic EPS	$ 1.24	$ 1.32	$ 2.07	$ 2.27
Diluted EPS	$ 1.24	$ 1.31	$ 2.06	$ 2.26
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	26,454	4,028	36,956	203,991