Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Balance, beginning of period (shares) at Dec. 31, 2013		40,536,879
Balance, beginning of period at Dec. 31, 2013	$ 204,148	$ 40,537	$ 337,887	$ (75,556)	$ (98,720)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options and stock awards (shares)		12,859
Exercise of stock options and stock awards	398	$ 13	385
Performance share and restricted stock unit (shares)		55,441
Performance shares and restricted stock units	2,935	$ 55	2,974	(94)
Net income	89,910			89,910
Director deferred stock awards	5,195		5,195
Pension plans and OPEB obligations	(19,672)				(19,672)
Cash flow hedge, net of tax of $448, $-, and $-	0
Common distributions, $1.425 per share 2014, $1.50 per share 2015, $1.50 per share 2016	(57,848)			(57,848)
Balance, end of period (shares) at Dec. 31, 2014		40,605,179
Balance, end of period at Dec. 31, 2014	225,066	$ 40,605	346,441	(43,588)	(118,392)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Performance share and restricted stock unit (shares)		75,534
Performance shares and restricted stock units	3,390	$ 76	3,406	(92)
Net income	31,714			31,714
Director deferred stock awards	701		701
Pension plans and OPEB obligations	3,889				3,889
Transfer of assets from REIT to subsidiary	(7)		(7)
Cash flow hedge, net of tax of $448, $-, and $-	0
Common distributions, $1.425 per share 2014, $1.50 per share 2015, $1.50 per share 2016	(61,017)			(61,017)
Balance, end of period (shares) at Dec. 31, 2015		40,680,713
Balance, end of period at Dec. 31, 2015	203,736	$ 40,681	350,541	(72,983)	(114,503)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Performance share and restricted stock unit (shares)		8,263
Performance shares and restricted stock units	3,971	$ 8	4,065	(102)
Net income	10,938			10,938
Director deferred stock awards	668		668
Pension plans and OPEB obligations	3,058				3,058
Repurchase of common stock (shares)		(169,625)
Repurchase of common stock	(5,956)	$ (170)		(5,786)
Cash flow hedge, net of tax of $448, $-, and $-	701				701
Common distributions, $1.425 per share 2014, $1.50 per share 2015, $1.50 per share 2016	(60,842)			(60,842)
Balance, end of period (shares) at Dec. 31, 2016		40,519,351
Balance, end of period at Dec. 31, 2016	$ 156,274	$ 40,519	$ 355,274	$ (128,775)	$ (110,744)