Subsequent events - Narrative (Details) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended		0 Months Ended	3 Months Ended
	Oct. 15, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Jan. 21, 2014 Subsequent Event [Member]	Dec. 31, 2013 Subsequent Event [Member]
Dividends Payable, Date Declared		Oct. 15, 2013					Jan. 21, 2014
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.175	$ 0.175	$ 0.175	$ 0.35	$ 0.35	$ 0.175
Annual Dividend Rate Per Share (in dollars per share)	$ 0.70					$ 0.70
Dividends Payable, Date of Record	Nov. 15, 2013					Feb. 14, 2014
Dividends Payable, Date to be Paid	Nov. 29, 2013					Feb. 28, 2014