Earnings per Share/Capital Stock: (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Additional disclosure
Stock options included in the calculation of diluted EPS (in shares)	176,048	456,318
Stock options not included in the calculation of diluted EPS (in shares)	0	110,013
Anti-dilutive stock options not included in the computation of diluted EPS (in shares)	0	75
Common Shares issued under DRP and the 2000 and 2008 Employee Plans	46,293	69,512
Value of Common Shares issued under DRP and the 2000 and 2008 Employee Plans	$ 625,000	$ 1,403,000
Common Shares repurchased in the open market under DRP and 401(k) Plan	42,597	221,932
Dividends paid	$ 6,838,000	$ 5,277,000
Quarterly dividends paid, per share of common stock (in dollars per share)	$ 0.355	$ 0.28
Restricted Stock Units
Additional disclosure
Restricted stock units outstanding (in shares)	145,208	147,078