Significant accounting policies Investment in joint venture (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2016	Jan. 31, 2015
Schedule of Equity Method Investments [Line Items]
date of investment in joint venture	Oct. 18, 2009
initial investment in joint venture	$ 5,900
Payments to acquire interest in JV	$ 2,000
Ownership percentage of joint venture	49.00%
Advances to joint venture	$ 3,900
Payments on loan from joint venture	$ 1,890	$ 0
Subsequent event date	Feb. 04, 2016
Payments to Acquire Businesses, Gross	$ 9,600
Income from joint venture	602	1,960
Equity Method Investment, Summarized Financial Information, Current Assets	8,274	13,820
Equity Method Investment, Summarized Financial Information, Noncurrent Assets	12,284	14,023
Equity Method Investment, Summarized Financial Information, Current Liabilities	2,438	4,499
Equity Method Investment, Summarized Financial Information, Noncurrent Liabilities	3,908	9,013
Equity Method Investment, Summarized Financial Information, Equity or Capital	14,212	14,331
Equity Method Investment, Summarized Financial Information, Revenue	22,228	40,397
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss)	3,465	8,451
Equity Method Investment, Summarized Financial Information, Income (Loss) from Continuing Operations before Extraordinary Items	1,938	6,397
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 1,228	$ 4,000