Stock-Based Compensation (Details) (USD $)	12 Months Ended										12 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended
	Dec. 31, 2011 plan Y	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Restricted stock units Y	Dec. 31, 2010 Restricted stock units	Dec. 31, 2009 Restricted stock units	Dec. 31, 2011 Stock options Y	Dec. 31, 2010 Stock options	Dec. 31, 2009 Stock options	Dec. 31, 2011 1995 Executive Incentive Compensation Plan	Dec. 31, 2011 1995 Executive Incentive Compensation Plan Restricted stock units Y	Dec. 31, 2011 1995 Non-Employee Directors' Stock Plan	Dec. 31, 2011 1995 Non-Employee Directors' Stock Plan Restricted stock units	May 31, 2008 Directors plan, May 1, 2008 Restricted stock units	Dec. 31, 2009 Directors plan, May 1, 2008 Restricted stock units	May 31, 2009 Directors plan, May 1, 2009 Restricted stock units	Dec. 31, 2010 Directors plan, May 1, 2009 Restricted stock units	Dec. 31, 2009 Directors plan, May 1, 2009 Restricted stock units	May 31, 2010 Directors plan, May 3, 2010 Restricted stock units	Dec. 31, 2011 Directors plan, May 3, 2010 Restricted stock units	Dec. 31, 2010 Directors plan, May 3, 2010 Restricted stock units	Jan. 31, 2006 Employees plan, January 24, 2006 Restricted stock units	Dec. 31, 2009 Employees plan, January 24, 2006 Restricted stock units	Jan. 31, 2007 Employees plan, January 23, 2007 Restricted stock units	Dec. 31, 2010 Employees plan, January 23, 2007 Restricted stock units	Dec. 31, 2009 Employees plan, January 23, 2007 Restricted stock units	Jan. 31, 2008 Employees plan, January 22, 2008 Restricted stock units	Dec. 31, 2011 Employees plan, January 22, 2008 Restricted stock units	Dec. 31, 2010 Employees plan, January 22, 2008 Restricted stock units	Dec. 31, 2009 Employees plan, January 22, 2008 Restricted stock units	Jan. 31, 2009 Employees plan, January 27, 2009 Restricted stock units	Dec. 31, 2011 Employees plan, January 27, 2009 Restricted stock units	Dec. 31, 2010 Employees plan, January 27, 2009 Restricted stock units	Dec. 31, 2009 Employees plan, January 27, 2009 Restricted stock units	Nov. 30, 2009 Employees plan, November 19, 2009 Restricted stock units	Dec. 31, 2011 Employees plan, November 19, 2009 Restricted stock units	Dec. 31, 2010 Employees plan, November 19, 2009 Restricted stock units	Dec. 31, 2009 Employees plan, November 19, 2009 Restricted stock units	Jan. 31, 2010 Employees plan, January 25, 2010 Restricted stock units	Dec. 31, 2011 Employees plan, January 25, 2010 Restricted stock units	Dec. 31, 2010 Employees plan, January 25, 2010 Restricted stock units	Sep. 30, 2010 Employees plan, September 22, 2010 Restricted stock units	Dec. 31, 2011 Employees plan, September 22, 2010 Restricted stock units	Dec. 31, 2010 Employees plan, September 22, 2010 Restricted stock units	May 31, 2011 Directors plan, May 2, 2011 Restricted stock units	Dec. 31, 2011 Directors plan, May 2, 2011 Restricted stock units	Apr. 30, 2011 Employees plan, April 26, 2011 Restricted stock units	Sep. 30, 2011 Employees plan, September 20, 2011 Restricted stock units
Stock-Based Compensation
Maximum number of shares authorized for issuance										8,000,000		600,000
Number of shares available for grant										1,564,039		212,808
Vesting period (in years)							3 years				3 years		1 year
Retirement age of employees (in years)											62
Granted (in shares)				37,442	42,000	137,625								16,000		16,000			16,000			93,100		101,700			130,950				106,625				15,000				1,000			25,000			20,192		3,750	13,500
Expense (Income)				$ 1,850,000	$ 3,297,000	$ 3,886,000	$ 2,000,000								$ 311,000		$ 145,000	$ 291,000		$ 165,000	$ 331,000		$ (191,000)		$ 41,000	$ 761,000		$ 68,000	$ 1,601,000	$ 1,371,000		$ 614,000	$ 667,000	$ 1,174,000		$ 12,000	$ 298,000	$ 169,000		$ 10,000	$ 20,000		$ 373,000	$ 194,000		$ 468,000	$ 29,000	$ 111,000
Restricted stock unit activity
Nonvested at the beginning of the period (in shares)				140,535	229,491	257,730
Granted (in shares)				37,442	42,000	137,625								16,000		16,000			16,000			93,100		101,700			130,950				106,625				15,000				1,000			25,000			20,192		3,750	13,500
Vested restricted Stock Units (in shares)				(113,136)	(124,424)	(153,283)
Forfeited (in shares)				(2,200)	(6,532)	(12,581)
Nonvested at the end of the period (in shares)				62,641	140,535	229,491
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)				$ 30.83	$ 34.45	$ 41.40
Granted (in dollars per share)				$ 29.61	$ 26.53	$ 26.13								$ 58.36		$ 27.28			$ 30.99			$ 33.85		$ 38.25			$ 45.95				$ 25.15				$ 31.90				$ 31.49			$ 23.47			$ 34.79		$ 32.10	$ 21.18
Vested (in dollars per share)				$ 33.55	$ 35.81	$ 38.46
Forfeited (in dollars per share)				$ 25.15	$ 35.23	$ 36.97
Nonvested at the end of the period (in dollars per share)				$ 25.39	$ 30.83	$ 34.45
Number of plans	2
Additional disclosures
Unrecognized stock-based compensation expense				600,000			4,400,000
Unrecognized stock-based compensation expense, period of recognition (in years)				1			2
Expiration period (in years)							P10Y
Stock option activity
Outstanding at the beginning of the period (in shares)							273,672	389,970	483,820
Granted (in shares)							617,500
Exercised (in shares)	(157,058)	(91,485)	(76,605)				(199,032)	(115,493)	(92,250)
Expired (in shares)								(805)	(1,600)
Forfeited/Expired (in shares)							(30,300)
Outstanding, at the end of the period (in shares)							661,840	273,672	389,970
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)							$ 16.46	$ 15.66	$ 15.39
Granted (in dollars per share)							$ 31.75
Exercised (in dollars per share)							$ 15.95	$ 13.77	$ 14.25
Expired (in dollars per share)								$ 16.33	$ 14.57
Cancelled/Expired (in dollars per share)							$ 30.92
Outstanding at the end of the period (in dollars per share)							$ 30.22	$ 16.46	$ 15.66
Intrinsic value, Outstanding at the beginning of the period							3,300,000	6,700,000	5,700,000
Intrinsic value, Outstanding at the end of the period							200,000	3,300,000	6,700,000
Intrinsic value of options exercised							2,200,000	1,700,000	1,400,000
Fair value (in dollars per share)							$ 10.90
Fair value assumptions
Dividend yield (as a percent)	2.50%
Volatility (as a percent)	40.60%
Risk-free interest rate (as a percent)	0.60%
Expected life (in years)	7
Net cash proceeds from the exercise of stock options							$ 2,400,000	$ 1,000,000	$ 1,000,000