Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Earnings Per Share [Abstract]
Net income		$ 36,506	$ 41,900	$ 116,273	$ 169,589
Weighted average common shares - basic		35,218,000	35,214,000	35,184,000	36,174,000
Equity based awards	[1]	231,000	183,000	209,000	180,000
Weighted average common shares - diluted		35,449,000	35,397,000	35,393,000	36,354,000
Basic		$ 1.04	$ 1.19	$ 3.30	$ 4.69
Diluted		$ 1.03	$ 1.18	$ 3.29	$ 4.66
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		844	0	1,454	0

[1] For the three and nine months ended October 31, 2016, there were 844 and 1,454 shares, respectively, excluded from the computation of diluted earnings per share because their effect would have been antidilutive. For the three and nine months ended October 31, 2015, there were no shares excluded from the computation of diluted earnings per share because their effect would have been antidilutive.