Investment in joint venture (Details) (USD $)	3 Months Ended		9 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013	Jan. 31, 2014
Schedule of Equity Method Investments [Line Items]
date of investment in joint venture			Oct. 18, 2009
initial investment in joint venture			$ 5,900,000
Payments to acquire interest in joint venture			2,000,000
Ownership percentage of joint venture	49.00%		49.00%
Payments for advance to affiliate			3,900,000
Income from joint venture	903,000	715,000	1,114,000	248,000
Equity Method Investment, Summarized Financial Information, Current Assets	14,451,000		14,451,000		13,034,000
Equity Method Investment, Summarized Financial Information, Noncurrent Assets	16,085,000		16,085,000		17,093,000
Equity Method Investment, Summarized Financial Information, Current Liabilities	4,184,000		4,184,000		2,921,000
Equity Method Investment, Summarized Financial Information, Noncurrent Liabilities	11,923,000		11,923,000		14,837,000
Equity Method Investment Summarized Financial Information, Equity	14,429,000		14,429,000		12,369,000
Equity Method Investment, Summarized Financial Information, Revenue			28,666,000	19,913,000
Equity Method Investment, Summarized Financial Information, Gross Profit			5,426,000	3,157,000
Equity Method Investment, Summarized Financial Information, Income from continuing operations			3,820,000	1,570,000
Equity Method Investment, Summarized Financial Information, Net income			$ 2,268,000	$ 516,000