Consolidated Statements of Stockholders' Equity (Unaudited) (USD $) In Thousands, except Share data	Total USD ($)	Common Stock Outstanding	Common Stock USD ($)	Value of Shares Held in Rabbi Trust at Cost USD ($)	Deferred Compensation Obligation USD ($)	Additional Paid-in Capital USD ($)	Retained Earnings USD ($)	Accumulated Other Comprehensive Loss USD ($)
Beginning balance at Dec. 31, 2012	$ 529,320		$ 225	$ (3,179)	$ 3,179	$ 269,950	$ 263,671	$ (4,526)
Common Stock, Shares, Outstanding at Dec. 31, 2012		22,774,009,000
Net income	25,010						25,010
Other comprehensive income (loss)	(2,871)							(2,871)
Common dividend declared	(10,070)						(10,070)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		30,029,000
Proceeds from exercise of stock options	744					744
Tax benefit related to equity award activity	312					312
Equity based compensation	1,389					1,389
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures		89,431,000
Restricted stock awards issued, net of awards surrendered	(668)		1			(669)
Stock Issued During Period Shares Direct Stock Purchase Plans		10,815,000
Shares issued under direct stock purchase plan	339					339
Deferred compensation obligation				(115)	115
Tax benefit related to deferred compensation distributions	100					100
Ending balance at Jun. 30, 2013	543,605		226	(3,294)	3,294	272,165	278,611	(7,397)
Common Stock, Shares, Outstanding at Jun. 30, 2013		22,904,284,000
Beginning balance at Dec. 31, 2013	591,540		235	(3,404)	3,404	305,179	293,560	(7,434)
Common Stock, Shares, Outstanding at Dec. 31, 2013	23,805,984	23,805,984,000
Net income	28,129						28,129
Other comprehensive income (loss)	5,741							5,741
Common dividend declared	(11,463)						(11,463)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		20,609,000
Proceeds from exercise of stock options	468					468
Tax benefit related to equity award activity	449					449
Equity based compensation	1,496					1,496
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures		60,495,000
Restricted stock awards issued, net of awards surrendered	(642)		1			(643)
Stock Issued During Period Shares Direct Stock Purchase Plans		16,984,000
Shares issued under direct stock purchase plan	643					643
Deferred compensation obligation				(124)	124
Tax benefit related to deferred compensation distributions	128					128
Ending balance at Jun. 30, 2014	$ 616,489		$ 236	$ (3,528)	$ 3,528	$ 307,720	$ 310,226	$ (1,693)
Common Stock, Shares, Outstanding at Jun. 30, 2014	23,904,072	23,904,072,000