Stock-Based Compensation (Summary of Activity Under Stock Option Plans) (Details) - USD ($)	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2016
Options Outstanding
Options outstanding at December 31, 2015 (shares)	156,057	212,038	212,038
Options exercised (shares)	0		(55,631)
Options forfeited (shares)	0		(350)
Options outstanding at September 30, 2016 (shares)	156,057	156,057	156,057
Options exercisable at September 30, 2016 (shares)	156,057		156,057
Options vested at June 30, 2016 (shares)	156,057		156,057
Weighted- Average Exercise Price Per Share
Options outstanding at December 31, 2015 (in USD per share)	$ 41.57	$ 40.47	$ 40.47
Options exercised (in USD per share)	0.00		36.99
Options forfeited (dollars per share)	0.00		44.32
Options outstanding at September 30, 2016 (in USD per share)	41.57	$ 41.57	41.57
Options exercisable at September 30, 2016 (in USD per share)	41.57		41.57
Options vested at June 30, 2016 (in USD per share)	$ 41.57		$ 41.57
Weighted-Average Remaining Contractual Life in Years
Weighted-Average Remaining Contractual Life in Year, Options outstanding	2 years 9 months 54 days	3 years 1 month 6 days
Options exercisable, Weighted-Average Remaining Contractual Life in Years (years)	2 years 9 months 54 days
Options vested, Weighted-Average Remaining Contractual Life in Years (years)	2 years 9 months 54 days
Aggregate Intrinsic Value
Options outstanding, Aggregate Intrinsic Value at December 31, 2015	$ 3,085,731
Options outstanding, Aggregate Intrinsic Value, at September 30, 2016	3,082,880	$ 3,085,731	$ 3,082,880
Options exercisable, Aggregate Intrinsic Value	3,082,880		3,082,880
Options vested, Aggregate Intrinsic Value	$ 3,082,880		$ 3,082,880