Stock-Based Compensation (Summary of Activity Under Stock Option Plans) (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2014		Mar. 31, 2014	Jun. 30, 2014
Options Outstanding
Beginning Balance (shares)	656,506		893,139	893,139
Options granted (shares)	0			0
Options exercised (shares)	(79,744)			(315,627)
Options forfeited (shares)	(20,150)			(20,900)
Ending Balance (shares)	556,612		656,506	556,612
Options exercisable (shares)	480,443			480,443
Options vested or expected to vest (shares)	554,327	[1]		554,327	[1]
Weighted-Average Exercise Price Per Share
Beginning Balance, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 42.44		$ 40.58	$ 40.58
Options granted, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 0.00			$ 0.00
Options exercised, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 48.10			$ 46.12
Options cancelled, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 59.85			$ 59.16
Ending Balance, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 40.96		$ 42.44	$ 40.96
Options exercisable, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 40.24			$ 40.24
Options vested or expected to vest, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 40.94	[1]		$ 40.94	[1]
Weighted-Average Remaining Contractual Life in Years
Options outstanding (years)			4 years 1 month	4 years 3 months
Options exercisable, Weighted-Average Remaining Contractual Life in Years (years)				3 years 9 months
Options vested or expected to vest, Weighted-Average Remaining Contractual Life in Years (years)				4 years 3 months	[1]
Aggregate Intrinsic Value
Options outstanding	$ 14,132,906		$ 13,184,080	$ 14,132,906
Options exercisable, Aggregate Intrinsic Value	12,543,846			12,543,846
Options vested or expected to vest, Aggregate Intrinsic Value	$ 14,085,234	[1]		$ 14,085,234	[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.