Share-Based Compensation Plans (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended					12 Months Ended	0 Months Ended	12 Months Ended										12 Months Ended
	Feb. 27, 2011	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009	May 18, 2011	Feb. 24, 2011	Dec. 31, 2011 Restricted Stock [Member]	May 22, 2011 Fair Value [Member]	Dec. 31, 2011 Stock Options [Member]	Dec. 31, 2011 2010 Employee Plan [Member]	Dec. 31, 2011 2009 Director Plan [Member]	Dec. 31, 2011 2003 Director Plan [Member]	Dec. 31, 2011 1995 Director Plan [Member]	Dec. 31, 2011 Key Employees [Member]	Dec. 31, 2011 Non-Employee Directors [Member]	Dec. 31, 2001 Non-Employee Directors [Member]	Dec. 31, 2000 Non-Employee Directors [Member]	Dec. 31, 1999 Non-Employee Directors [Member]	Dec. 31, 2011 Employees And Non-Employee Directors [Member]	Dec. 31, 2010 Employees And Non-Employee Directors [Member]	Dec. 31, 2009 Employees And Non-Employee Directors [Member]	Dec. 31, 2011 Share Based Compensation [Member]	Dec. 31, 2010 Share Based Compensation [Member]	Dec. 31, 2009 Share Based Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares, authorized		200,000,000	200,000,000							4,000,000	37,439	500,000				40,000	30,000	26,000
Remaining shares		3,464,709									35,192	431,000
Share-based compensation expense		$ 17,693	$ 14,726	$ 13,296
Income tax benefit recorded		5,576	4,391	4,152
Share-based compensation awards granted		226,700	150,055	131,700			226,700		345,600
Share-based compensation grant exercise price					$ 90.49	$ 86.62
Weighted-average grant-date fair value of options granted	$ 21.85	$ 21.85	$ 22.06	$ 17.54				$ 21.89
Aggregate intrinsic value of options exercised		11,845	3,305	7,547
Cash received from the exercised share options		32,519
Tax benefit realized from the options exercised		4,071
Tax benefit from stock options vested		1,714
Fair value of shares vested		5,981	5,057	3,758
Unrecognized compensation cost		22,648
Unrecognized compensation cost expected to be recognized over a weighted-average period, years		2.8
Common shares, issued		668	0	488
Restricted shares issued														977,980	58,157
Restricted shares cancelled		160,160
Common shares acquired																			201,287	7,281	4,688	33,225	4,531	12,489
Additional paid-in capital due to tax benefits from dividends on restricted shares		217	124	99
Common stock, value		2,970	397	1,039															17,951	618	325
Aggregate values of issuances		$ 56	$ 0	$ 37
Percentage of options and restricted shares granted		33.00%								20.00%		33.00%	50.00%
Vesting period on options and restricted shares, years		three years								five years		three y	two years.
Expiration period for options exercisable at market value, years		ten years