STATEMENTS OF COMMON STOCKHOLDER'S EQUITY - USD ($) $ in Thousands	Total	Common stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2012	$ 1,176,955	$ 0	$ 843,186	$ 335,101	$ (1,332)
Beginning Balance (in shares) at Dec. 31, 2012		100
Comprehensive income:
Net income	95,177			95,177
Other comprehensive income	171				171
Common dividends declared to parent	(70,889)			(70,889)
Contribution of capital by parent	162,277		162,277
Ending Balance at Dec. 31, 2013	1,363,691	$ 0	1,005,463	359,389	(1,161)
Ending Balance (in shares) at Dec. 31, 2013		100
Comprehensive income:
Net income	129,852			129,852
Other comprehensive income	172				172
Common dividends declared to parent	(93,243)			(93,243)
Contribution of capital by parent	160,000		160,000
Ending Balance at Dec. 31, 2014	$ 1,560,472	$ 0	1,165,463	395,998	(989)
Ending Balance (in shares) at Dec. 31, 2014	100	100
Comprehensive income:
Net income	$ 127,263			127,263
Other comprehensive income	(292)				(292)
Common dividends declared to parent	(85,254)			(85,254)
Contribution of capital by parent	205,760		205,760
Ending Balance at Dec. 31, 2015	$ 1,807,949	$ 0	$ 1,371,223	$ 438,007	$ (1,281)
Ending Balance (in shares) at Dec. 31, 2015	100	100