Earnings Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reconciliation of number of shares used in calculation of basic and diluted earnings per share
Weighted average number of common shares outstanding	86,100,000	85,300,000	85,900,000	86,700,000
Effect of non-participatory equity compensation (in shares)	40,000	36,000	40,000	36,000
Weighted average number of common shares outstanding, including effect of dilutive securities	86,100,000	85,300,000	85,900,000	86,800,000