Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of number of shares used in calculation of basic and diluted earnings per share
Weighted average number of common shares outstanding	84,900,000	85,900,000	85,200,000	85,900,000
Effect of non-participatory equity compensation (in shares)	40,000	45,000	40,000	45,000
Weighted average number of common shares outstanding, including effect of dilutive securities	84,900,000	86,000,000	85,300,000	85,900,000