Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Change in unrealized appreciation (depreciation) of investments, tax expense (benefit)	$ (2,941)	$ (1,285)	$ 2,825