Stock-Based Compensation (Summary of Activity Under Stock Option Plans) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Options Outstanding
Beginning Balance (shares)	393,347
Options granted (shares)	0
Options exercised (shares)	(141,097)
Options forfeited (shares)	(850)
Ending Balance (shares)	251,400		393,347
Options exercisable (shares)	237,412
Options vested or expected to vest (shares)	250,980	[1]
Weighted- Average Exercise Price Per Share
Beginning Balance, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 40.72
Options granted	$ 0.00
Options exercised	$ 39.93
Options forfeited	$ 43.00
Ending Balance, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 41.06		$ 40.72
Options exercisable, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 40.42
Options vested or expected to vest, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 41.05	[1]
Weighted-Average Remaining Contractual Life in Years
Options outstanding	3 years 8 months		3 years 9 months
Options exercisable, Weighted-Average Remaining Contractual Life in Years (years)	3 years 4 months
Options vested or expected to vest, Weighted-Average Remaining Contractual Life in Years (years)	3 years 8 months	[1]
Aggregate Intrinsic Value
Options outstanding	$ 10,344,139		$ 16,019,130
Options exercisable, Aggregate Intrinsic Value	9,920,540
Options vested or expected to vest, Aggregate Intrinsic Value	$ 10,331,431	[1]

[1] In addition to the vested options, we expect a portion of the unvested options to vest at some point in the future. Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options.