SUMMARY OF QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Consolidated quarterly financial data                      
Interest income $ 45,903 $ 43,934 $ 40,140 $ 44,015 $ 36,842 $ 36,107 $ 35,722 $ 33,761 $ 173,992 $ 142,432 $ 132,377
Interest expense 4,258 4,536 4,563 4,581 4,376 4,683 4,664 4,739 17,938 18,462 19,604
NET INTEREST INCOME 41,645 39,398 35,577 39,434 32,466 31,424 31,058 29,022 156,054 123,970 112,773
Provision for loan and lease losses 5,004 2,489 1,814 5,186 2,074 2,233 904 185 14,493 5,396 2,859
NET INTEREST INCOME AFTER PROVISION FOR LOAN AND LEASE LOSSES 36,641 36,909 33,763 34,248 30,392 29,191 30,154 28,837 141,561 118,574 109,914
Non interest income 10,485 11,301 10,802 24,921 7,717 7,806 9,485 22,986 57,509 47,994 42,519
Non interest expenses 32,166 33,534 31,866 32,541 26,847 28,238 27,165 31,074 130,107 113,324 108,118
INCOME BEFORE INCOME TAX EXPENSE 14,960 14,676 12,699 26,628 11,262 8,759 12,474 20,749 68,963 53,244 44,315
Income tax expense (benefit) 4,960 4,848 4,359 8,893 3,844 3,119 4,154 6,961 23,060 18,078 15,528
NET INCOME $ 10,000 $ 9,828 $ 8,340 $ 17,735 $ 7,418 $ 5,640 $ 8,320 $ 13,788 $ 45,903 $ 35,166 $ 28,787
Class A Common Stock                      
Basic earnings per share:                      
Basic earnings per share (in dollars per share) $ 0.48 $ 0.47 $ 0.40 $ 0.86 $ 0.36 $ 0.27 $ 0.40 $ 0.66 $ 2.22 $ 1.70 $ 1.39
Diluted earnings per share:                      
Diluted earnings per share (in dollars per share) 0.48 0.47 0.40 0.85 0.36 0.27 0.40 0.66 2.22 1.70 1.38
Dividends declared per common share:                      
Dividend declared common stock, per share (in dollars per share) 0.209 0.209 0.209 0.198 0.198 0.198 0.198 0.187 0.825 0.781 0.737
Class B Common Stock                      
Basic earnings per share:                      
Basic earnings per share (in dollars per share) 0.44 0.43 0.37 0.78 0.33 0.25 0.37 0.65 2.02 1.55 1.32
Diluted earnings per share:                      
Diluted earnings per share (in dollars per share) 0.44 0.43 0.37 0.77 0.33 0.25 0.36 0.64 2.01 1.54 1.32
Dividends declared per common share:                      
Dividend declared common stock, per share (in dollars per share) $ 0.190 $ 0.190 $ 0.190 $ 0.180 $ 0.180 $ 0.180 $ 0.180 $ 0.170 $ 0.750 $ 0.710 $ 0.670