Stock-Based Compensation Plans (Details) (USD $)	12 Months Ended										0 Months Ended	12 Months Ended	0 Months Ended
	Dec. 31, 2012 plan	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 1994 Plan	Dec. 31, 2012 1994 Plan Granted on 3 Feb 2011	Dec. 31, 2012 1994 Plan Granted on 2 Feb 2010	Dec. 31, 2012 1995 Plan Granted on 15 Feb 2011	Dec. 31, 2012 Stock Bonus Plan	Dec. 31, 2011 Stock Bonus Plan	Dec. 31, 2010 Stock Bonus Plan	Feb. 06, 2013 Restricted Stock Units	Dec. 31, 2012 Restricted Stock Units	Feb. 06, 2013 Independent directors Restricted Stock Units
Stock-Based Compensation Plans
Number of stock-based incentive plans	1
Number of stock option plans superseded	2
Restricted stock unit activity
Awarded (in shares)											359,371	361,000	9,975
Vested (in shares)												(95,000)
Forfeited (in shares)												(2,000)
Outstanding at the end of the period (in shares)												264,000
Outstanding and expected to vest at the end of the period (in shares)												259,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 31.15
Awarded (in dollars per share)											$ 31.96	$ 33.23
Vested (in dollars per share)												$ 33.23
Forfeited (in dollars per share)	$ 32.25											$ 33.23
Outstanding at the end of the period (in dollars per share)	$ 31.58	$ 31.15										$ 33.23
Outstanding and expected to vest at the end of the period (in dollars per share)												$ 33.23
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 5,347,000	$ 8,053,000										$ 8,657,000
Outstanding and expected to vest at end of the period (in dollars)	5,261,000											8,485,000
Closing price per share (in dollars per share)												$ 32.79
Total intrinsic value of awards vested (in dollars)												3,100,000
Black-Scholes option pricing model assumptions for options granted
Number of Options Granted (in shares)					1,362,000	148,000	30,000
Risk Free Interest Rate (as a percent)					2.62%	2.93%	2.92%
Dividend Yield (as a percent)					1.75%	1.62%	1.76%
Expected Life					6 years 2 months 12 days	6 years 6 months	6 years 7 months 6 days
Volatility (as a percent)					39.00%	36.00%	38.00%
Exercise price for options granted, low end of range (in dollars per share)					$ 29.66
Exercise price for options granted, high end of range (in dollars per share)					$ 32.63
Exercise Price (in dollars per share)						$ 24.75	$ 29.58
Weighted Average Fair Value (in dollars per share)					$ 10.33	$ 8.46	$ 10.49
Non-Qualified Stock Options activity
Outstanding at the beginning of the period (in shares)	2,134,000
Exercised (in shares)	(186,000)
Forfeited (in shares)	(41,000)
Outstanding at the end of the period (in shares)	1,907,000	2,134,000
Outstanding and expected to vest at the end of the period (in shares)	1,882,000
Exercisable at the end of the period (in shares)	1,081,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 31.15
Exercised (in dollars per share)	$ 26.55
Forfeited (in dollars per share)	$ 32.25											$ 33.23
Outstanding at the end of the period (in dollars per share)	$ 31.58	$ 31.15										$ 33.23
Outstanding and expected to vest at end of the period (in dollars per share)	$ 31.60
Exercisable at end of the period (in dollars per share)	$ 33.20
Weighted-Average Remaining Contractual Life
Outstanding at the end of the period	3 years 9 months 18 days	3 years 1 month 6 days
Outstanding and expected to vest at end of the period	3 years 8 months 12 days
Exercisable at end of the period	2 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	5,347,000	8,053,000										8,657,000
Outstanding and expected to vest at end of the period (in dollars)	5,261,000											8,485,000
Exercisable at end of the period (in dollars)	2,592,000
Closing price of share (in dollars per share)	$ 32.79
Total intrinsic value of options exercised (in dollars)	1,100,000	100,000	1,400,000
Number of Shares, Unvested Stock Options
Unvested at the beginning of the period (in shares)	1,242,000
Vested (in shares)	(397,000)
Forfeited (in shares)	(19,000)
Unvested at the end of the period (in shares)	826,000	1,242,000
Weighted-Average Grant-Date Fair Value, Unvested Stock Options
Unvested at the beginning of the period (in dollars per share)	$ 10.11
Vested (in dollars per share)	$ 9.87
Forfeited (in dollars per share)	$ 8.88
Unvested at the end of the period (in dollars per share)	$ 10.25	$ 10.11
Unrecognized compensation cost and vesting period
Unrecognized compensation costs related to unvested share-based compensation arrangements				18,100,000
Weighted-average period for recognition of unrecognized stock-based compensation expense				2 years 1 month 6 days
Other disclosures
Shares issued and committed to issue								9,000	12,000	8,000
Stock-based compensation expense recognized in operating expenses	$ 10,205,000	$ 6,133,000	$ 3,338,000					$ 500,000	$ 700,000	$ 400,000
The anniversary year of employment during which shares are issued to the employee under the plan				4 years				10 years