Net Income Per Share: (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	141,000	135,000
Net income	$ 7,601	$ 8,073
Weighted average number of common shares outstanding (for basic calculation)	13,956,000	13,692,000
Dilutive securities	362,000	364,000
Weighted average common and common equivalent shares outstanding (for diluted calculation)	14,318,000	14,056,000
EPS - basic	$ 0.54	$ 0.59
EPS - diluted	$ 0.53	$ 0.57