Performance Incentive Plan (Other Grants) (Details)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Other share grants under the 2017 Plan:
Restricted shares granted (in shares)	28,127
Restricted shares granted, weighted average share price (in dollars per share) | $ / shares	$ 53.47
Shares available under the 2017 Plan for grant, end of period (in shares)	1,092,770
Directors’ fees
Other share grants under the 2017 Plan:
Restricted shares granted (in shares)	13,448
Restricted shares granted, weighted average share price (in dollars per share) | $ / shares	$ 53.62
Deferred directors’ fees
Other share grants under the 2017 Plan:
Restricted shares granted (in shares)	14,679
Restricted shares granted, weighted average share price (in dollars per share) | $ / shares	$ 53.34