EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
EARNINGS PER SHARE
Net income	$ 17,735	$ 13,788
Weighted average shares outstanding	20,904,000	20,859,000
Effect of dilutive securities (in shares)	105,000	77,000
Average shares outstanding including dilutive securities	21,009,000	20,936,000
Basic earnings per share:
Basic earnings per share	$ 0.78	$ 0.65
Diluted earnings per share:
Diluted earnings per share	$ 0.77	$ 0.64
Antidilutive stock options (in shares)	10,500	14,250
Average antidilutive stock options (in shares)	10,500	14,250
Class A Common Stock
EARNINGS PER SHARE
Cash dividend premium per share (as a percent)	10.00%
Basic earnings per share:
Basic earnings per share	$ 0.86	$ 0.66
Diluted earnings per share:
Diluted earnings per share	0.85	0.66
Class B Common Stock
Basic earnings per share:
Basic earnings per share	0.78	0.65
Diluted earnings per share:
Diluted earnings per share	$ 0.77	$ 0.64