Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 72,871	$ 115,834	$ 67,015	$ 24,025	$ 75,962	$ 54,716	$ 47,602	$ 10,681	$ 279,745	$ 188,961	$ 216,001
Distributed and undistributed (earnings) to unvested restricted stock									(4,285)	(2,930)	(4,172)
Distributed and undistributed earnings to common shareholders — Basic									$ 275,460	$ 186,031	$ 211,829
Weighted average shares outstanding — Basic									22,393	22,225	22,243
Weighted average shares outstanding — Diluted									22,393	22,225	22,243
Earnings per common share - Basic (in usd per share)									$ 12.30	$ 8.37	$ 9.52
Earnings per common share - Diluted (in usd per share)	$ 3.20	$ 5.09	$ 2.95	$ 1.06	$ 3.36	$ 2.42	$ 2.11	$ 0.47	$ 12.30	$ 8.37	$ 9.52