CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Capital	Retained earnings	Accumulated Other Comprehensive Income/(Loss)	Treasury Stock
Balance at Dec. 31, 2014	$ 394,214	$ 1,815	$ 72,405	$ 377,970	$ (14,529)	$ (43,447)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	30,196	0	0	30,196	0	0
Other comprehensive income (loss)	5,128	0	0	0	5,128	0
Treasury Stock, Value, Acquired, Cost Method	(8,698)					(8,698)
Contribution of shares to ESOP	715	2	713	0	0	0
Employee Stock Ownership Plan (ESOP), Cash Contributions to ESOP	1,294	0	278	0	0	1,016
Cash Dividends	(12,533)	0	0	(12,533)	0	0
Balance at Dec. 31, 2015	410,316	1,817	73,396	395,633	(9,401)	(51,129)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,413	0	0	38,413	0	0
Other comprehensive income (loss)	(4,763)	0	0	0	(4,763)	0
Treasury Stock, Value, Acquired, Cost Method	(19,396)	0	0	0	0	(19,396)
Contribution of shares to ESOP	684	3	681	0	0	0
Employee Stock Ownership Plan (ESOP), Cash Contributions to ESOP	1,361	0	448	0	0	913
Cash Dividends	(12,220)	0	0	(12,220)	0	0
Balance at Dec. 31, 2016	414,395	1,820	74,525	421,826	(14,164)	(69,612)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,131	0	0	29,131	0	0
Other comprehensive income (loss)	(540)	0	0	0	(540)	0
Treasury Stock, Value, Acquired, Cost Method	(503)	0	0	0	0	(503)
Contribution of shares to ESOP	706	2	704	0	0	0
Employee Stock Ownership Plan (ESOP), Cash Contributions to ESOP	1,062	0	395	0	0	667
Cash Dividends	(30,682)	0	0	(30,682)	0	0
Balance at Dec. 31, 2017	$ 413,569	$ 1,822	$ 75,624	$ 420,275	$ (14,704)	$ (69,448)