Net Income Per Share: (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	295,000	559,000	189,000	742,000
Net income	$ 9,261	$ 8,975	$ 26,827	$ 20,943
Weighted average number of common shares outstanding (for basic calculation)	13,932,000	13,489,000	13,826,000	13,605,000
Dilutive securities	252,000	263,000	343,000	233,000
Weighted average common and common equivalent shares outstanding (for diluted calculation)	14,184,000	13,752,000	14,169,000	13,838,000
EPS - basic	$ 0.66	$ 0.67	$ 1.94	$ 1.54
EPS - diluted	$ 0.65	$ 0.65	$ 1.89	$ 1.51