Equity And Comprehensive Income (Detailed Activities Of Equity) (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
DECEMBER 31, 2010, Shares			45,599,036
DECEMBER 31, 2010, Values			$ 1,166,996
Common stock issuances, values			8,683
Net income (loss)	4,013	(993)	72,367	63,467	112,353	101,198
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax			640
FSIRS unrealized loss, net of tax			(1,950)
Amounts reclassified to net income, net of tax (Note 4)	182		363		423
Dividends declared Common: $0.53 per share			(24,656)
JUNE 30, 2011, Shares	45,879,314		45,879,314		45,879,314
JUNE 30, 2011, Values	1,222,443		1,222,443		1,222,443
Dividends declared per share	$ 0.2650	$ 0.2500	$ 0.5300	$ 0.5000	$ 1.0300	$ 0.9750
Common Stock [Member]
DECEMBER 31, 2010, Shares			45,599,000
DECEMBER 31, 2010, Values			47,229
Common stock issuances, shares			280,000
Common stock issuances, values			280
JUNE 30, 2011, Shares	45,879,000		45,879,000		45,879,000
JUNE 30, 2011, Values	47,509		47,509		47,509
Additional Paid-In Capital [Member]
DECEMBER 31, 2010, Values			807,885
Common stock issuances, values			8,403
JUNE 30, 2011, Values	816,288		816,288		816,288
Accumulated Other Comprehensive Income (Loss) [Member]
DECEMBER 31, 2010, Values			(30,784)
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax			640
FSIRS unrealized loss, net of tax			(1,950)
Amounts reclassified to net income, net of tax (Note 4)			363
JUNE 30, 2011, Values	(31,731)		(31,731)		(31,731)
Retained Earnings [Member]
DECEMBER 31, 2010, Values			343,131
Net income (loss)			72,604
Dividends declared Common: $0.53 per share			(24,656)
JUNE 30, 2011, Values	391,079		391,079		391,079
Non-controlling Interest [Member]
DECEMBER 31, 2010, Values			(465)
Net income (loss)			(237)
JUNE 30, 2011, Values	$ (702)		$ (702)		$ (702)