CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2011	$ 521,153	$ 93,300	$ 187,071	$ 241,296	$ (514)
Balance (in shares) at Dec. 31, 2011		933,000
Comprehensive income:
Net income	49,951			49,951
Other comprehensive income	77				77
Common dividends declared to parent	(56,871)			(56,871)
Contribution of capital by parent	2,796		2,796
Ending Balance at Dec. 31, 2012	517,106	93,300	189,867	234,376	(437)
Balance (in shares) at Dec. 31, 2012		933,000
Comprehensive income:
Net income	59,468			59,468
Other comprehensive income	76				76
Common dividends declared to parent	(31,345)			(31,345)
Contribution of capital by parent	58,977		58,977
Ending Balance at Dec. 31, 2013	604,282	93,300	248,844	262,499	(361)
Balance (in shares) at Dec. 31, 2013	933,000	933,000
Comprehensive income:
Net income	70,642			70,642
Other comprehensive income	76				76
Common dividends declared to parent	(50,743)			(50,743)
Contribution of capital by parent	73,432		73,432
Ending Balance at Dec. 31, 2014	$ 697,689	$ 93,300	$ 322,276	$ 282,398	$ (285)
Balance (in shares) at Dec. 31, 2014	933,000	933,000