Supplementary Insurance Information Unallocated Corporate Items (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unallocated Corporate Items [Line Items]
Net Investment Income	$ 33,983	$ 34,609	$ 28,821
Corporate and Other Operating Expenses	$ 17,338	$ 24,448	$ 14,559