Stock Option Plan (Details) (Stock Options [Member], USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Options [Member]
Options, shares [Roll Forward]
Outstanding, beginning of period (in shares)	77,000
Granted (in shares)	0
Exercised (in shares)	8,000
Forfeited or expired (in shares)	0
Outstanding, end of period (in shares)	69,000	77,000
Exercisable, end of period (in shares)	69,000
Options, weighted average exercise price [Roll Forward]
Outstanding, beginning of period (in dollars per share)	$ 22.82
Granted (in dollars per share)	$ 0
Exercised (in dollars per share)	$ 14.83
Forfeited or expired (in dollars per share)	$ 0
Outstanding, end of period (in dollars per share)	$ 23.75	$ 22.82
Exercisable, end of period (in dollars per share)	$ 23.75
Weighted-average remaining contractual term, outstanding	3 years 9 months 29 days
Weighted-average remaining contractual term, exercisable	3 years 9 months 29 days
Options outstanding, aggregate intrinsic value	$ 596
Options exercisable, aggregate intrinsic value	596
Intrinsic value of share exercised	$ 141	$ 85	$ 0