Dividends and earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2015	Oct. 31, 2014	Oct. 31, 2013
Dividends and earnings per share [Abstract]
Dividends declared (amount)									$ 8,130	$ 8,276	$ 10,830
Dividends declared per share	$ 0.30	$ 0.30	$ 0.30	$ 0.30	$ 0.30	$ 0.30	$ 0.30	$ 0.30	$ 1.20	$ 1.20	$ 1.56