CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Common Stock [Member]	Additional Paid In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Total
Balance at Dec. 31, 2009	$ 93,300	$ 146,505	$ 253,935	$ (666)	$ 493,074
Balance (in shares) at Dec. 31, 2009	933,000
Comprehensive income:
Net income			42,749		42,749
Other comprehensive income				76	76
Comprehensive income					42,825
Common dividends declared to parent			(73,787)		(73,787)
Contribution of capital by parent		40,566			40,566
Balance at Dec. 31, 2010	93,300	187,071	222,897	(590)	502,678
Balance (in shares) at Dec. 31, 2010	933,000
Comprehensive income:
Net income			51,006		51,006
Other comprehensive income				76	76
Comprehensive income					51,082
Common dividends declared to parent			(32,607)		(32,607)
Contribution of capital by parent		0			0
Balance at Dec. 31, 2011	93,300	187,071	241,296	(514)	521,153
Balance (in shares) at Dec. 31, 2011	933,000				933,000
Comprehensive income:
Net income			49,951		49,951
Other comprehensive income				77	77
Comprehensive income					50,028
Common dividends declared to parent			(56,871)		(56,871)
Contribution of capital by parent		2,796			2,796
Balance at Dec. 31, 2012	$ 93,300	$ 189,867	$ 234,376	$ (437)	$ 517,106
Balance (in shares) at Dec. 31, 2012	933,000				933,000