Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2015	Jul. 31, 2014
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0	0	0
Net income	$ 76,412	$ 39,328	$ 127,689	$ 52,795
Weighted average common shares - basic	36,506,000	38,244,000	36,661,000	38,191,000
Equity based awards	109,000	124,000	168,000	151,000
Weighted average common shares - diluted	36,615,000	38,368,000	36,829,000	38,342,000
Basic	$ 2.09	$ 1.03	$ 3.48	$ 1.38
Diluted	$ 2.09	$ 1.03	$ 3.47	$ 1.38