Unaudited Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Consolidated Balance Sheets (Parenthetical) [Abstract]
Amortized cost of fixed maturity securities-available-for-sale	$ 7,699.6	$ 7,390.0
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	42,342,304	42,077,825
Common Stock, no par value	$ 0	$ 0