Earnings (loss) per common share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Weighted average common shares outstanding - basic	195,151	193,949	194,814	191,958
Effect of dilutive performance share awards	18	351	19	349
Weighted average common shares outstanding - diluted	195,169	194,300	194,833	192,307
Shares excluded from the calculation of diluted earnings per share	0	0	0	0