Performance Incentive Plan (Other Grants) (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Other share grants under the 2017 Plan:
Restricted shares granted (in shares)	40,581
Restricted shares granted, weighted average share price (in dollars per share) | $ / shares	$ 41.84
Shares available under the 2017 Plan for grant, end of period (in shares)	1,471,231
Directors’ fees
Other share grants under the 2017 Plan:
Restricted shares granted (in shares)	15,712
Restricted shares granted, weighted average share price (in dollars per share) | $ / shares	$ 41.75
Deferred directors’ fees
Other share grants under the 2017 Plan:
Restricted shares granted (in shares)	24,869
Restricted shares granted, weighted average share price (in dollars per share) | $ / shares	$ 41.89