Earnings (loss) per common share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	194,805	192,060	194,643	190,946
Effect of dilutive performance share awards	33	599	32	597
Weighted average common shares outstanding - diluted	194,838	192,659	194,675	191,543
Shares excluded from the calculation of diluted earnings per share	0	0	0	0