Net Income Per Share: (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,000	7,000	3,000	145,000
Net income	$ 9,149	$ 9,493	$ 16,750	$ 17,566
Weighted average number of common shares outstanding (for basic calculation)	14,179,000	13,852,000	14,067,000	13,772,000
Dilutive securities	441,000	405,000	417,000	394,000
Weighted average common and common equivalent shares outstanding (for diluted calculation)	14,620,000	14,257,000	14,484,000	14,166,000
EPS - basic	$ 0.65	$ 0.69	$ 1.19	$ 1.28
EPS - diluted	$ 0.63	$ 0.67	$ 1.16	$ 1.24