Subsequent event (Details) (USD $)	0 Months Ended	3 Months Ended	0 Months Ended	3 Months Ended
	Mar. 20, 2014	Mar. 31, 2014	Apr. 30, 2014 Subsequent event	Mar. 31, 2014 Subsequent event
Subsequent event
Quarterly cash dividend (in dollars per share)	$ 0.125		$ 0.125
Dividends payable date declared				Apr. 30, 2014
Dividends payable date of record		Feb. 28, 2014		May 30, 2014
Dividends payable date to be paid				Jun. 20, 2014