Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2015	Oct. 31, 2014	Oct. 31, 2015	Oct. 31, 2014
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0	0	0
Net income	$ 41,900	$ 41,700	$ 169,589	$ 94,495
Weighted average common shares - basic	35,214,000	38,253,000	36,174,000	38,212,000
Equity based awards	183,000	180,000	180,000	164,000
Weighted average common shares - diluted	35,397,000	38,433,000	36,354,000	38,376,000
Basic	$ 1.19	$ 1.09	$ 4.69	$ 2.47
Diluted	$ 1.18	$ 1.09	$ 4.66	$ 2.46