Earnings Per Share (Details) - shares	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Basic computation	50,321,000	50,318,000	49,869,000	49,416,000	48,902,000	48,487,000	48,451,000	48,386,000		49,984,562		48,557,599	48,298,896
Performance and restricted share awards (1)									22,044	252,909	[1]	97,722	176,166
Diluted computation										50,237,471		48,655,321	48,475,062

[1] Performance share awards are included in diluted weighted average number of shares outstanding based upon what would be issued if the end of the most recent reporting period was the end of the term of the award.