STATEMENTS OF CHANGES IN COMMON EQUITY AND COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified		Total	Common Stock [Member]	Other Paid-In Capital and Premium on Common Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2010		$ 426,885	$ 5,848	$ 200,841	$ (9,120)	$ 229,316
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		52,889				52,889
Other Comprehensive (Loss) Income, Net of Tax	[1]	(3,009)			(3,009)
Cash Dividends Declared – Common Stock		(12,664)				(12,664)
Additional Investment by Shareholder		0		0
Excess Tax Benefit from Restricted Stock Plan		85		85
Balance at Dec. 31, 2011		464,186	5,848	200,926	(12,129)	269,541
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		58,241				58,241
Other Comprehensive (Loss) Income, Net of Tax	[1]	(1,156)			(1,156)
Cash Dividends Declared – Common Stock		0				0
Additional Investment by Shareholder		0		0
Excess Tax Benefit from Restricted Stock Plan		124		124
Balance at Dec. 31, 2012		521,395	5,848	201,050	(13,285)	327,782
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		62,236				62,236
Other Comprehensive (Loss) Income, Net of Tax	[1]	2,416			2,416
Cash Dividends Declared – Common Stock		0				0
Additional Investment by Shareholder		25,000		25,000
Excess Tax Benefit from Restricted Stock Plan		(78)		(78)
Additional Statement Information [Abstract]
Combined statutory rate		41.00%
Balance at Dec. 31, 2013		$ 610,969	$ 5,848	$ 225,972	$ (10,869)	$ 390,018

[1] Determined using a combined statutory tax rate of 41%.