Equity (Details2) (USD $)	1 Months Ended	12 Months Ended		1 Months Ended
	Jan. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2015	Dec. 31, 2008
Stock Based Compensation Plans
Number of shares of common stock that have been reserved for awards (in shares)					600,000
Restricted Stock [Member]
Stock Based Compensation Plans
Number of shares cancelled (in shares)	640
Shares vested due to retirement of former SVP Marketing and Strategic Planning			18,180
Compensation expense related to the vesting of stock awards		$ 3,241,000	$ 2,591,000
Compensation expense related to the accelerated vesting			457,000
Total compensation cost which will be recognized ratably over the remaining vesting period		4,195,000
Restricted stock activity
Outstanding at the beginning of the year (in shares)	214,168	165,149	195,449
Granted (in shares)		95,000	34,400
Vested (in shares)		(45,981)	(64,700)
Outstanding at the end of the year (in shares)		214,168	165,149
Weighted Average Price
Weighted average remaining contractual life of options exercisable			3 years
Restricted Stock [Member] | Vesting over Three Year Period from Grant Date [Member]
Stock Based Compensation Plans
Vesting period				3 years
Restricted stock activity
Granted (in shares)				65,750
Price per share				$ 44.45
Restricted Stock [Member] | Vesting Through December 31 2016 [Member]
Weighted Average Price
Options scheduled to vest (in shares)		5,000
Restricted Stock [Member] | Vesting Through December 31 2017 [Member]
Weighted Average Price
Options scheduled to vest (in shares)		5,000
Restricted Stock [Member] | Subsequent Event [Member]
Stock Based Compensation Plans
Number of shares cancelled (in shares)		640
Vesting period		3 years
Restricted stock activity
Granted (in shares)		65,750
Price per share		$ 44.45
Restricted Stock [Member] | Grant Date Price 36.81 [Member] | Vesting over Three Year Period from Grant Date [Member]
Stock Based Compensation Plans
Vesting period		3 years
Restricted stock activity
Granted (in shares)		59,000
Price per share		$ 36.81
Restricted Stock [Member] | Grant Date Price 38.43 [Member] | Vesting over Three Year Period from Grant Date [Member]
Stock Based Compensation Plans
Vesting period		3 years
Restricted stock activity
Granted (in shares)		3,000
Price per share		$ 38.43
Restricted Stock [Member] | Grant Date Price 40.05[Member] | Vesting over Three Year Period from Grant Date [Member]
Stock Based Compensation Plans
Vesting period		3 years
Restricted stock activity
Granted (in shares)		15,000
Price per share		$ 40.05
Restricted Stock [Member] | Grant Date Price 40.05[Member] | Vesting Date 9 June2015 [Member]
Restricted stock activity
Granted (in shares)		10,500
Price per share		$ 40.05
Restricted Stock [Member] | Grant Date Price 41.34 [Member] | Vesting Date 12 November 2015 [Member]
Restricted stock activity
Granted (in shares)		7,500
Price per share		$ 41.34
Restricted Stock [Member] | Grant Date Price 46.54 [Member] | Vesting over Three Year Period from Grant Date [Member]
Stock Based Compensation Plans
Vesting period			3 years
Restricted stock activity
Granted (in shares)			8,400
Price per share			$ 46.54
Restricted Stock [Member] | Grant Date Price 41.83 [Member] | Vesting over Three Year Period from Grant Date [Member]
Stock Based Compensation Plans
Vesting period			3 years
Restricted stock activity
Granted (in shares)			6,000
Price per share			$ 41.83
Restricted Stock [Member] | Grant Date Price 36.26 [Member] | Vesting Date 1 June 2016 [Member]
Restricted stock activity
Granted (in shares)			20,000
Price per share			$ 36.26
Employee Stock Option [Member]
Stock Based Compensation Plans
Compensation expense related to the vesting of stock awards		12,000
Fair value assumptions
Expected life		3 years
Volatility rate (as a percent)		0.21%
Risk free interest rate (as a percent)		0.66%
Expected dividend yield (as a percent)		5.31%
Fair value of option (in dollars per share)		$ 2.96
Nonqualified stock option activity
Outstanding at the beginning of the year (in shares)		73,334	95,334
Granted (in shares)		15,000	0
Exercised (in shares)		(45,000)	(22,000)
Outstanding at the end of the year (in shares)		43,334	73,334
Options exercisable at end of the period (in shares)		28,334	73,334
Weighted Average Price
Outstanding at the beginning of the year (in dollars per share)		$ 23.97	$ 23.93
Granted (in dollars per share)		$ 38.43
Exercised (in dollars per share)		$ 23.79	$ 23.79
Outstanding at the end of the year (in dollars per share)		$ 29.16	$ 23.97
Exercisable at the end of the period (in dollars per share)		$ 24.25	$ 23.97
Aggregate intrinsic value of exercisable options at the end of the year			536,000
Weighted average remaining contractual life of options exercisable			2 years 8 months 12 days
Options Exercised (in shares)		45,000	22,000
Weighted Average Exercise Price (in dollars per share)		$ 23.79	$ 23.79
Value of options exercised		1,071,000	523,000
Market value on the date of exercise		1,840,000	865,000
Weighted average exercise price of the options (in dollars per share)		$ 29.16	$ 23.97
Remaining compensation expense to be recognized related to the future service period of unvested outstanding stock options
2015		15,000
2016		15,000
2017		$ 2,000
Employee Stock Option [Member] | Vesting over Three Year Period from Grant Date [Member]
Stock Based Compensation Plans
Vesting period		3 years
Employee Stock Option [Member] | Vesting Through December 31 2015 [Member]
Weighted Average Price
Options scheduled to vest (in shares)		5,000
Employee Stock Option [Member] | Vesting Beyond 2017 [Member]
Weighted Average Price
Options scheduled to vest (in shares)		0