Statements of Common Stockholder's Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Common Stock, Shares, Issued - Beginning Balance at Dec. 31, 2012		23,416,000
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Stock Issued During Period, Shares, New Issues		0
Common Stock, Shares, Issued - Ending Balance at Dec. 31, 2013		23,416,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2012		$ 23,416	$ 39,575	$ 257,887	$ (1,420)
Stockholders' Equity Attributable to Parent [Abstract]
Stock Issued During Period, Value, New Issues		0	0
Net income	$ 30,173			30,173
Non-cash Dividend to Parent Company				(8,000)
Other Comprehensive Income (Loss), Net of Tax	223				223
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2013	$ 341,854	$ 23,416	39,575	280,060	(1,197)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Stock Issued During Period, Shares, New Issues		0
Common Stock, Shares, Issued - Ending Balance at Dec. 31, 2014	23,416,396	23,416,000
Stockholders' Equity Attributable to Parent [Abstract]
Stock Issued During Period, Value, New Issues		$ 0	0
Net income	$ 33,562			33,562
Non-cash Dividend to Parent Company				0
Other Comprehensive Income (Loss), Net of Tax	(622)				(622)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2014	$ 374,794	$ 23,416	39,575	313,622	(1,819)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Stock Issued During Period, Shares, New Issues		0
Common Stock, Shares, Issued - Ending Balance at Dec. 31, 2015	23,416,396	23,416,000
Stockholders' Equity Attributable to Parent [Abstract]
Stock Issued During Period, Value, New Issues		$ 0	0
Net income	$ 45,174
Non-cash Dividend to Parent Company				(28,501)
Other Comprehensive Income (Loss), Net of Tax	512				512
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2015	$ 391,979	$ 23,416	$ 39,575	$ 330,295	$ (1,307)