Stock-Based Compensation (Summary Of Stock Options Under The 2007 Plan) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Shares
Options outstanding, December 31, 2016 | shares	91,000
Granted | shares	0
Exercised | shares	(28,000)
Forfeited and expired | shares	0
Options outstanding, December 31, 2017 | shares	63,000
Vested and expected to vest as of December 31, 2017 | shares	63,000
Exercisable as of December 31, 2017 | shares	63,000
Weighted average exercise price
Options outstanding, December 31, 2016 | $ / shares	$ 63.84
Granted | $ / shares	0.00
Exercised | $ / shares	66.08
Forfeited and expired | $ / shares	0.00
Options outstanding, December 31, 2017 | $ / shares	62.86
Vested and expected to vest as of December 31, 2017 | $ / shares	62.86
Exercisable as of December 31, 2017 | $ / shares	$ 62.86
Additional Disclosures
Options outstanding, weighted average remaining contractual term (years)	3 years 9 months 18 days
Vested and expected to vest, weighted average remaining contractual term (years)	3 years 9 months 18 days
Exercisable, weighted average remaining contractual term (years)	3 years 9 months 18 days
Options outstanding, aggregate intrinsic value | $	$ 13,446
Vested and expected to vest, aggregate intrinsic value | $	13,446
Exercisable, aggregate intrinsic value | $	$ 13,446