Equity (Details 2) (USD $)		12 Months Ended			1 Months Ended			12 Months Ended
	Dec. 31, 2008	Dec. 31, 2011 Restricted stock	Dec. 31, 2010 Restricted stock	Dec. 31, 2011 Restricted stock $ 28.70 per share	Jan. 31, 2012 Restricted stock $ 31.77 per share Issuance of shares	Jan. 31, 2012 Restricted stock $ 31.77 per share Issuance of shares Vesting on June 15, 2015	Jan. 31, 2012 Restricted stock $ 31.77 per share Issuance of shares Vesting on January 10, 2016	Dec. 31, 2010 Restricted stock $ 25.95 per share	Dec. 31, 2010 Restricted stock $ 25.04 per share	Dec. 31, 2010 Restricted stock $ 26.53 per share	Dec. 31, 2010 Restricted stock $ 26.59 per share	Dec. 31, 2011 Stock Options Y	Dec. 31, 2010 Stock Options Y
Stock Based Compensation Plans
Number of shares of common stock that have been reserved for awards (in shares)	600,000
Number of shares granted (in shares)		6,000	208,591	6,000	14,000			4,000	1,000	11,030	92,900
Additional shares granted (in shares)						30,000	12,200			99,661
Price per share				$ 28.70	$ 31.77	$ 31.77	$ 31.77	$ 25.95	$ 25.04	$ 26.53
Vesting period (in years)		three-year			five-year			three-year	three-year	three-year	five-year
Vesting period of additional shares granted (in years)										five-year
Restricted stock activity
Outstanding at the beginning of the year (in shares)		217,317	84,866
Granted (in shares)		6,000	208,591	6,000	14,000			4,000	1,000	11,030	92,900
Vested (in shares)		(58,183)	(76,140)
Outstanding at the end of the year (in shares)		165,134	217,317
Compensation expense for the year		$ 1,450,000	$ 1,210,000
Total compensation cost		3,892,000										10,000
Nonqualified stock option activity
Outstanding at the beginning of the year (in shares)												185,334	197,000
Exercised (in shares)												(5,000)	(11,666)
Outstanding at the end of the year (in shares)												180,334	185,334
Exercisable at the end of the period (in shares)												175,334	175,334
Weighted Average Price
Outstanding at the beginning of the year (in dollars per share)												$ 23.34	$ 22.88
Exercised (in dollars per share)												$ 23.79	$ 15.62
Outstanding at the end of the year (in dollars per share)												$ 23.33	$ 23.34
Exercisable at the end of the period (in dollars per share)												$ 23.29	$ 23.27
Aggregate intrinsic value of exercisable options at the end of the year												1,327,000
Weighted average remaining contractual life of options exercisable (in years)												3.5
Options Exercised (in shares)												5,000	11,666
Weighted Average Exercise Price (in dollars per share)												$ 23.79	$ 15.62
Stock-based compensation plans, additional disclosures
Option value												119,000	182,000
Market value												$ 152,000	$ 315,000
Weighted average exercise price of the options (in dollars per share)												$ 23.33	$ 23.34
Weighted average remaining contractual life of options outstanding (in years)												0.0	0.1