Stock Based Compensation (Outstanding Employee Stock Awards) (Details) - $ / shares	May 17, 2018	May 18, 2017	May 24, 2016	Jan. 03, 2014	Sep. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested Shares (in shares)					1,034,995
Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value (in dollars per share)					$ 22.36	$ 21.69
Unvested Shares (in shares)					1,034,995	868,437
Deferred Stock Awards | Deferred Stock Award, Granted January 3, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)				72,969
Grant Date Fair Value (in dollars per share)				$ 16.45
Unvested Shares (in shares)					16,416
Deferred Stock Awards | Deferred Stock Award, Granted January 3, 2014 | Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				20.00%
Deferred Stock Awards | Deferred Stock Award, Granted January 3, 2014 | Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				20.00%
Deferred Stock Awards | Deferred Stock Award, Granted January 3, 2014 | Share-based Compensation Award, Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				20.00%
Deferred Stock Awards | Deferred Stock Award, Granted January 3, 2014 | Share-based Compensation Award, Tranche Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				20.00%
Deferred Stock Awards | Deferred Stock Award, Granted January 3, 2014 | Share-based Compensation Award, Tranche Five
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				20.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 24, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)			208,003
Grant Date Fair Value (in dollars per share)			$ 19.91
Unvested Shares (in shares)					60,591
Deferred Stock Awards | Deferred Stock Award, Granted May 24, 2016 | Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 24, 2016 | Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 24, 2016 | Share-based Compensation Award, Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 24, 2016 | Share-based Compensation Award, Tranche Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 18, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)		219,863
Grant Date Fair Value (in dollars per share)		$ 21.38
Unvested Shares (in shares)					123,507
Deferred Stock Awards | Deferred Stock Award, Granted May 18, 2017 | Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 18, 2017 | Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 18, 2017 | Share-based Compensation Award, Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 18, 2017 | Share-based Compensation Award, Tranche Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 17, 2018 Deferred Stock Award Independent Directors | Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)	31,388
Grant Date Fair Value (in dollars per share)	$ 17.84
Unvested Shares (in shares)					31,388
Deferred Stock Awards | Deferred Stock Award, Granted May 17, 2018 Deferred Stock Award Independent Directors | Share-based Compensation Award, Tranche One | Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	100.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 17, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)	302,706
Grant Date Fair Value (in dollars per share)	$ 17.84
Unvested Shares (in shares)					239,777
Deferred Stock Awards | Deferred Stock Award, Granted May 17, 2018 | Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 17, 2018 | Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 17, 2018 | Share-based Compensation Award, Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Deferred Stock Awards | Deferred Stock Award, Granted May 17, 2018 | Share-based Compensation Award, Tranche Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Performance Share Awards | Performance Share Program Award, Granted May 24, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)			0
Grant Date Fair Value (in dollars per share)			$ 23.02
Unvested Shares (in shares)					99,337
Performance Share Awards | Performance Share Program Award, Granted May 18, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)		0
Grant Date Fair Value (in dollars per share)		$ 30.45
Unvested Shares (in shares)					143,335
Performance Share Awards | Performance Share Program Award, Granted May 17, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net Shares Granted (in shares)	0
Grant Date Fair Value (in dollars per share)	$ 23.52
Unvested Shares (in shares)					320,644