Consolidated Statements of Changes in Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Class A Common Stock [Member]	Retained Earnings [Member] Class B Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2013	$ 176,472	$ 3,580	$ 1,976	$ 11,932	$ 180,747			$ (21,763)
Net income	16,237	12,741	3,496		16,237
Other comprehensive income, net of tax:
Unrealized holding (losses) gains arising during period, net of taxes	1,509							1,509
Unrealized holding (losses) gains arising during period, net of taxes	1,509
Accretion of unrealized losses on securities transferred to held-to-maturity net of taxes	2,524							2,524
Amortization of prior service cost and loss included in net periodic benefit cost	169							169
Conversion of class B common stock to class A common stock		9
Conversion of class B common stock to class A common stock			(9)
Stock options exercised	329	11		318
Cash dividends		(1,290)	(356)			$ (1,290)	$ (356)
Ending balance at Sep. 30, 2014	195,594	3,600	1,967	12,250	195,338			(17,561)
Beginning balance at Dec. 31, 2014	192,500	3,601	1,967	12,292	200,411			(25,771)
Net income	17,050	13,392	3,658		17,050
Other comprehensive income, net of tax:
Unrealized holding (losses) gains arising during period, net of taxes	(2)
Unrealized holding (losses) gains arising during period, net of taxes	(104)							(104)
Accretion of unrealized losses on securities transferred to held-to-maturity net of taxes	2,697							2,697
Amortization of prior service cost and loss included in net periodic benefit cost	639							639
Cash dividends		(1,296)	(354)			$ (1,296)	$ (354)
Ending balance at Sep. 30, 2015	$ 211,132	$ 3,601	$ 1,967	$ 12,292	$ 215,811			$ (22,539)