Subsequent events - Narrative (Details) (USD $)	0 Months Ended	3 Months Ended			0 Months Ended	3 Months Ended
	Jul. 15, 2014	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2013	Oct. 21, 2014 Subsequent Event [Member]	Sep. 30, 2014 Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends payable, date declared		Jul. 15, 2014				Oct. 21, 2014
Common stock, dividends, per share, declared (in dollars per share)	$ 0.18	$ 0.180		$ 0.175	$ 0.18
Annual dividend rate per share (in dollars per share)	$ 0.72		$ 0.70			$ 0.72
Dividends payable, date of record	Aug. 15, 2014					Nov. 14, 2014
Dividends payable, date to be paid	Aug. 29, 2014					Nov. 28, 2014