CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income
Balance at Dec. 31, 2009	$ 787,024	$ 395	$ 807,527	$ (90,228)	$ 59,605	$ 9,725
Shares, Balance at Dec. 31, 2009		39,567		3,563
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Net Income	77,376	0	0	0	77,376	0
Other comprehensive income:
Foreign currency translation adjustment	111	0	0	0	0	111
Reclassification of net gains on derivative instruments from OCI to net income, net of tax	(1,188)	0	0	0	0	(1,188)
Reclassification of deferred tax liability on net gains on derivative instruments	0
Pension and postretirement medical liability adjustment, net of tax	(134)	0	0	0	0	(134)
Stock based compensation, value	5,920	3	6,336	(419)	0	0
Stock based compensation, shares		232		14
Issuance of shares, value	235	0	15		0	0
Issuance of shares, shares		0
Issuance of shares, value, treasury stock reissued				220
Issuance of shares, shares, treasury stock reissued				(7)
Dividends on common stock	(48,997)	0	0	0	(48,997)	0
Balance at Dec. 31, 2010	820,347	398	813,878	(90,427)	87,984	8,514
Shares, Balance at Dec. 31, 2010		39,799		3,570
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Net Income	92,556	0	0	0	92,556	0
Other comprehensive income:
Foreign currency translation adjustment	25	0	0	0	0	25
Reclassification of net gains on derivative instruments from OCI to net income, net of tax	(730)	0	0	0	0	(730)
Reclassification of deferred tax liability on net gains on derivative instruments	(3,572)					(3,572)
Pension and postretirement medical liability adjustment, net of tax	(581)	0	0	0	0	(581)
Stock based compensation, value	2,669	0	2,762	(93)	0	0
Stock based compensation, shares		42		3
Issuance of shares, value	307	0	60		0	0
Issuance of shares, shares		0
Issuance of shares, value, treasury stock reissued				247
Issuance of shares, shares, treasury stock reissued				(10)
Dividends on common stock	(51,909)	0	0	0	(51,909)	0
Balance at Dec. 31, 2011	859,112	398	816,700	(90,273)	128,631	3,656
Shares, Balance at Dec. 31, 2011		39,841		3,563
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Net Income	98,406	0	0	0	98,406	0
Other comprehensive income:
Foreign currency translation adjustment	(54)	0	0	0	0	(54)
Reclassification of net gains on derivative instruments from OCI to net income, net of tax	(732)	0	0	0	0	(732)
Reclassification of deferred tax liability on net gains on derivative instruments	0
Pension and postretirement medical liability adjustment, net of tax	(553)	0	0	0	0	(553)
Stock based compensation, value	3,133	1	3,925	(793)	0	0
Stock based compensation, shares		136		22
Issuance of shares, value	28,966	9	28,593		0	0
Issuance of shares, shares		815
Issuance of shares, value, treasury stock reissued				364
Issuance of shares, shares, treasury stock reissued				(14)
Dividends on common stock	(54,246)	0	0	0	(54,246)	0
Balance at Dec. 31, 2012	$ 934,032	$ 408	$ 849,218	$ (90,702)	$ 172,791	$ 2,317
Shares, Balance at Dec. 31, 2012		40,792		3,571