Stock-Based Compensation (Summary of Activity Under Stock Option Plans) (Details) (USD $)	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2014		Jun. 30, 2014	Sep. 30, 2014
Options Outstanding
Beginning Balance (shares)	556,612		893,139	893,139
Options granted (shares)	0			0
Options exercised (shares)	(42,689)			(358,316)
Options forfeited (shares)	(2,099)			(22,999)
Ending Balance (shares)	511,824		556,612	511,824
Options exercisable (shares)	453,994			453,994
Options vested or expected to vest (shares)	510,089	[1]		510,089	[1]
Weighted-Average Exercise Price Per Share
Beginning Balance, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 40.96		$ 43.23	$ 43.23
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)	$ 34.37			$ 44.72
Options cancelled, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 36.26			$ 57.07
Ending Balance, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 41.53		$ 40.96	$ 41.53
Options exercisable, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 41.12			$ 41.12
Options vested or expected to vest, Weighted-Average Exercise Price Per Share, (dollars per share)	$ 41.52	[1]		$ 41.52	[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 7 months
Options vested or expected to vest, Weighted-Average Remaining Contractual Life in Years (years)	4 years 1 month	[1]
Aggregate Intrinsic Value
Options outstanding	$ 6,976,521		$ 14,132,906	$ 6,976,521
Options exercisable, Aggregate Intrinsic Value	6,394,886			6,394,886
Options vested or expected to vest, Aggregate Intrinsic Value	$ 6,959,072	[1]		$ 6,959,072	[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.