Stock-Based Compensation (Summary of Activity Under Stock Option Plans) (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Options Outstanding
Options outstanding at December 31, 2015 (shares)		212,038
Options exercised (shares)		(13,672)
Options forfeited (shares)		0
Options outstanding at March 31, 20165 (shares)		198,366	212,038
Options exercisable at March 31, 2016 (shares)		198,366
Options vested at March 31, 2016 (shares)	[1]	198,366
Weighted- Average Exercise Price Per Share
Options outstanding at December 31, 2015 (in USD per share)		$ 40.47
Options exercised (in USD per share)		41.25
Options forfeited (dollars per share)		0.00
Options outstanding at March 31, 2016 (in USD per share)		40.31	$ 40.47
Options exercisable at March 31, 2016 (in USD per share)		40.31
Options vested at March 31, 2016 (in USD per share)	[1]	$ 40.31
Weighted-Average Remaining Contractual Life in Years
Weighted-Average Remaining Contractual Life in Year, Options outstanding		3 years 3 months	3 years 2 months
Options exercisable, Weighted-Average Remaining Contractual Life in Years (years)		3 years 3 months
Options vested, Weighted-Average Remaining Contractual Life in Years (years)	[1]	3 years 3 months
Aggregate Intrinsic Value
Options outstanding, Aggregate Intrinsic Value at December 31, 2015		$ 2,557,193
Options outstanding, Aggregate Intrinsic Value, at Mach 31, 2016		3,934,582	$ 2,557,193
Options exercisable, Aggregate Intrinsic Value		3,934,582
Options vested, Aggregate Intrinsic Value	[1]	$ 3,934,582

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