STATEMENTS OF CHANGES IN COMMON STOCK EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss), Net of Tax	Treasury Stock
Balances at beginning of period at Dec. 31, 2010	$ 810,375	$ 65,265	$ 305,068	$ 810,858	$ (33,177)	$ (337,639)
Balances at beginning of period (in shares) at Dec. 31, 2010		65,265,060				22,693,995
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted common stock grants and deferred compensation (in shares)		118,110
Restricted common stock grants and deferred compensation	3,205	118	3,087
Performance share awards vested (in shares)		40,895
Performance share awards vested	628	41	587
Stock awards withheld for taxes (in shares)		(23,702)
Stock awards withheld for taxes	(739)	(24)	(715)
Forfeited restricted common stock (in shares)		(2,200)
Forfeited restricted common stock	(2)	(2)
Deferred taxes on stock incentive plan	1,112		1,112
Stock options exercised (in shares)		53,910
Stock options exercised	692	54	638
Net income	103,539			103,539
Other comprehensive income (loss)	(44,328)				(44,328)
Dividends, Common Stock, Cash	27,223			27,223
Treasury stock acquired, at cost (in shares)						2,798,924
Treasury stock acquired, at cost	(87,008)					(87,008)
Balances at end of period at Dec. 31, 2011	760,251	65,452	309,777	887,174	(77,505)	(424,647)
Balances at end of period (in shares) at Dec. 31, 2011		65,452,073				25,492,919
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted common stock grants and deferred compensation (in shares)		87,428
Restricted common stock grants and deferred compensation	1,778	87	1,691
Performance share awards vested (in shares)		174,038
Performance share awards vested	1,193	174	1,019
Stock awards withheld for taxes (in shares)		(52,778)
Stock awards withheld for taxes	(1,822)	(52)	(1,770)
Forfeited restricted common stock (in shares)		(88,100)
Forfeited restricted common stock	(1,294)	(88)	(1,206)
Deferred taxes on stock incentive plan	1,101		1,101
Stock options exercised (in shares)		32,336
Stock options exercised	414	32	382
Net income	90,846			90,846
Other comprehensive income (loss)	11,421				11,421
Dividends, Common Stock, Cash	38,889			38,889
Balances at end of period at Dec. 31, 2012	824,999	65,605	310,994	939,131	(66,084)	(424,647)
Balances at end of period (in shares) at Dec. 31, 2012	65,520,551	65,604,997				25,492,919
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted common stock grants and deferred compensation (in shares)		96,279
Restricted common stock grants and deferred compensation	2,798	96	2,702
Performance share awards vested (in shares)		64,275
Performance share awards vested	849	64	785
Stock awards withheld for taxes (in shares)		(23,808)
Stock awards withheld for taxes	(811)	(23)	(788)
Forfeited restricted common stock (in shares)		(1,549)
Forfeited restricted common stock	(1)	(1)
Deferred taxes on stock incentive plan	427		427
Stock options exercised (in shares)		15,000
Stock options exercised	192	15	177
Grants of share based compensation (in shares)		4,431
Grants of share based compensation	150	4	146
Net income	88,583			88,583
Other comprehensive income (loss)	68,696				68,696
Dividends, Common Stock, Cash	42,049			42,049
Treasury stock acquired, at cost (in shares)	0
Balances at end of period at Dec. 31, 2013	$ 943,833	$ 65,760	$ 314,443	$ 985,665	$ 2,612	$ (424,647)
Balances at end of period (in shares) at Dec. 31, 2013	65,639,091	65,759,625				25,492,919