Net Income Per Share: (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 6,657	$ 8,685
Weighted average number of common shares outstanding (for basic calculation)	15,097,000	14,507,000
Dilutive securities	298,000	546,000
Weighted average common and common equivalent shares outstanding (for diluted calculation)	15,395,000	15,053,000
EPS - basic	$ 0.44	$ 0.60
EPS - diluted	$ 0.43	$ 0.58
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	237,000	142,000