Unaudited Interim Statements of Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income	Total equity
Balance at Dec. 31, 2013		$ 2,500	$ 901,422	$ 764,846	$ 70,867	$ 1,739,635
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Distribution to parent				(267,000)		(267,000)
Comprehensive income:
Net income	$ 134,929			134,929		134,929
Other comprehensive income (loss), net of taxes	23,149				23,149	23,149
Total comprehensive income						158,078
Balance at Jun. 30, 2014		2,500	901,422	632,775	94,016	1,630,713
Balance at Dec. 31, 2014		2,500	901,422	673,613	84,622	1,662,157
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Distribution to parent				(270,000)		(270,000)
Comprehensive income:
Net income	110,612			110,612		110,612
Other comprehensive income (loss), net of taxes	$ (18,361)				(18,361)	(18,361)
Total comprehensive income						92,251
Balance at Jun. 30, 2015		$ 2,500	$ 901,422	$ 514,225	$ 66,261	$ 1,484,408