EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
EARNINGS PER SHARE
Net income	$ 10,071	$ 8,340	$ 30,088	$ 26,075
Weighted average shares outstanding	21,151,000	20,947,000	20,918,000	20,956,000
Effect of dilutive securities (in shares)	79,000	11,000	78,000	10,000
Average shares outstanding including dilutive securities	21,230,000	20,958,000	20,996,000	20,966,000
Diluted earnings per share:
Antidilutive stock options (in shares)	2,500	10,000	2,500	10,000
Average antidilutive stock options (in shares)	1,166	7,500	584	8,150
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	$ 0.48	$ 0.40	$ 1.45	$ 1.26
Diluted earnings per share:
Diluted earnings per share	0.48	0.40	1.45	1.26
Class B Common Stock
Basic earnings per share:
Basic earnings per share	0.44	0.37	1.32	1.14
Diluted earnings per share:
Diluted earnings per share	$ 0.44	$ 0.37	$ 1.32	$ 1.14