Stock-Based Compensation Plans (Narrative) (Details) (USD $)	3 Months Ended			6 Months Ended					6 Months Ended
	Jun. 30, 2011	Mar. 31, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 2007 Plan [Member]	May 31, 2011 2007 Plan [Member]	May 31, 2009 2007 Plan [Member]	Jun. 30, 2010 Executive Officer [Member]
Shares initially approved for issuance						500,000
Shares additionally approved for issuance							2,860,000	325,000
Shares additionally available for future grants	2,946,092			2,946,092
Compensation cost charged to income for stock options	$ 103,000		$ 421,000	$ 376,000	$ 998,000
Compensation cost charged to income for restricted share awards	819,000		643,000	1,600,000	1,400,000
Weighted average grant date fair value per share of options granted		$ 32.59		$ 33.57	$ 35.84				$ 16.65
Aggregate intrinsic value of options exercised				769,000	2,200,000
Restricted Stock Units, Granted		446		75,785	131,656
Unrecognized compensation cost related to non-vested share based arrangements	$ 7,800,000			$ 7,800,000