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 Loss
Balance June 30, 2015 at Dec. 31, 2013		23,805,984
Balance June 30, 2014 at Dec. 31, 2013	$ 591,540		$ 235	$ (3,404)	$ 3,404	$ 305,179	$ 293,560	$ (7,434)
Net income	28,129						28,129
Other comprehensive loss	5,741							5,741
Common dividend declared ($0.52 per share)	(11,463)						(11,463)
Common stock issued for acquisition	0
Proceeds from exercise of stock options, net of cash paid		20,609
Proceeds from exercise of stock options, net of cash paid	468					468
Tax benefit related to equity award activity	449					449
Stock based compensation	1,496					1,496
Restricted stock awards issued, net of awards surrendered		60,495
Restricted stock awards issued, net of awards surrendered	(642)		1			(643)
Shares issued under direct stock purchase plan		16,984
Shares issued under direct stock purchase plan	643					643
Deferred compensation and other retirement benefit obligations				(124)	124
Tax benefit related to deferred compensation distributions	128					128
Balance December 31, 2014 at Jun. 30, 2014	$ 616,489		236	(3,528)	3,528	307,720	310,226	(1,693)
Balance December 31, 2013 at Jun. 30, 2014		23,904,072
Balance June 30, 2015 at Dec. 31, 2014	23,998,738	23,998,738
Balance June 30, 2014 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 loss	(4)							(4)
Common dividend declared ($0.52 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					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
Tax benefit related to deferred compensation distributions	165					165
Balance December 31, 2014 at Jun. 30, 2015	$ 743,317		$ 259	$ (3,785)	$ 3,785	$ 401,437	$ 343,757	$ (2,136)
Balance December 31, 2013 at Jun. 30, 2015	26,158,826	26,158,826