Net Income Per Share: (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 13,570	$ 5,878	$ 23,256	$ 12,535
Weighted average number of common shares outstanding (for basic calculation)	15,781,000	15,242,000	15,738,000	15,170,000
Dilutive securities	571,000	120,000	564,000	269,000
Weighted average common and common equivalent shares outstanding (for diluted calculation)	16,352,000	15,362,000	16,302,000	15,439,000
EPS - basic	$ 0.86	$ 0.39	$ 1.48	$ 0.83
EPS - diluted	$ 0.83	$ 0.38	$ 1.43	$ 0.81
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	33,000	266,000	16,000	235,000