Income Taxes (Provision/Benefit for Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current [Abstract]
Federal	$ 54,915	$ (3,824)	$ (13,320)
State	(163)	(1,039)	14,252
Total current	54,752	(4,863)	932
Deferred [Abstract]
Federal	12,699	53,642	77,750
State	(20,209)	26,859	9,661
Total deferred	(7,510)	80,501	87,411
Income Tax Expense (Benefit), Total	47,242	75,638	88,343
Income taxes charged (credited) to shareholders' equity of Frontier [Abstract]
Utilization of the benefits arising from restricted stock	1,910	2,937
Deferred income taxes (benefits) arising from the recognition of additional pension/OPEB liability	132,432	(58,551)	(97,409)
Total income taxes charged (credited) to shareholders' equity of Frontier	134,342	(55,614)	(97,409)
Total income taxes	$ 181,584	$ 20,024	$ (9,066)