Earnings Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	86,100,000	85,400,000	85,900,000
Effect of non-participatory equity compensation (in shares)	40,000	40,000	40,000	40,000
Weighted average number of common shares outstanding, including effect of dilutive securities	85,000,000	86,100,000	85,500,000	85,900,000