Net Income Per Share: (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 16,266	$ 6,428	$ 39,522	$ 18,963
Weighted average number of common shares outstanding (for basic calculation)	15,894,000	15,319,000	15,790,000	15,220,000
Dilutive securities	681,000	169,000	619,000	277,000
Weighted average common and common equivalent shares outstanding (for diluted calculation)	16,575,000	15,488,000	16,409,000	15,497,000
EPS - basic	$ 1.02	$ 0.42	$ 2.50	$ 1.25
EPS - diluted	$ 0.98	$ 0.42	$ 2.41	$ 1.22
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	211,000	44,000	235,000