Net Income Per Share: (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	7,000	922,000	145,000	748,000
Net income	$ 9,493	$ 7,713	$ 17,566	$ 11,968
Weighted average number of common shares outstanding (for basic calculation)	13,852,000	13,469,000	13,772,000	13,665,000
Dilutive securities	405,000	188,000	394,000	223,000
Weighted average common and common equivalent shares outstanding (for diluted calculation)	14,257,000	13,657,000	14,166,000	13,888,000
EPS - basic	$ 0.69	$ 0.57	$ 1.28	$ 0.88
EPS - diluted	$ 0.67	$ 0.56	$ 1.24	$ 0.86