Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock Outstanding	Common Stock	Value of Shares Held in Rabbi Trust at Cost	Deferred Compensation and Other Retirement Benefit Obligations	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance June 30, 2016 at Dec. 31, 2014		23,998,738
Balance June 30, 2015 at Dec. 31, 2014	$ 640,527		$ 237	$ (3,666)	$ 3,666	$ 311,978	$ 330,444	$ (2,132)
Net income	26,910						26,910
Other comprehensive income	(4)							(4)
Common dividend declared ($0.58 per share)	(13,597)						(13,597)
Common stock issued for acquisition		2,052,137
Common stock issued for acquisition	86,415		21			86,394
Proceeds from exercise of stock options, net of cash paid		40,314
Proceeds from exercise of stock options, net of cash paid	311		0			311
Tax benefit related to equity award activity	546					546
Stock based compensation	1,362					1,362
Restricted stock awards issued, net of awards surrendered		36,101
Restricted stock awards issued, net of awards surrendered	(645)		1			(646)
Shares issued under direct stock purchase plan		31,536
Shares issued under direct stock purchase plan	1,327					1,327
Deferred compensation and other retirement benefit obligations				(119)	119
Increase (Decrease) in Deferred Compensation	0
Tax benefit related to deferred compensation distributions	165					165
Balance December 31, 2015 at Jun. 30, 2015	743,317		259	(3,785)	3,785	401,437	343,757	(2,136)
Balance December 31, 2014 at Jun. 30, 2015		26,158,826
Balance June 30, 2016 at Dec. 31, 2015		26,236,352
Balance June 30, 2015 at Dec. 31, 2015	771,463		260	(3,958)	3,958	405,486	368,169	(2,452)
Net income	38,985						38,985
Other comprehensive income	6,035							6,035
Common dividend declared ($0.58 per share)	(15,256)						(15,256)
Common stock issued for acquisition	0
Proceeds from exercise of stock options, net of cash paid		6,652
Proceeds from exercise of stock options, net of cash paid	144					144
Tax benefit related to equity award activity	327					327
Stock based compensation	1,633					1,633
Restricted stock awards issued, net of awards surrendered		42,967
Restricted stock awards issued, net of awards surrendered	(673)		1			(674)
Shares issued under direct stock purchase plan		23,916
Shares issued under direct stock purchase plan	1,060					1,060
Deferred compensation and other retirement benefit obligations				(155)	155
Tax benefit related to deferred compensation distributions	179					179
Balance December 31, 2015 at Jun. 30, 2016	$ 803,897		$ 261	$ (4,113)	$ 4,113	$ 408,155	$ 391,898	$ 3,583
Balance December 31, 2014 at Jun. 30, 2016		26,309,887