Summary of Investments (Net Realized Investment Gains and Losses and Proceeds) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	$ 3,954	$ 2,055
Available-for-sale Securities [Abstract]
Proceeds from sales	5,059	1,968
Gross realized gains	2,222	921
Fixed maturities: | Available-for-sale
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	1,995	516
Fixed maturities: | Change in fair value
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	371	273
Fixed maturities: | Sales
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	57	0
Equity securities: | Available-for-sale
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	1,410	984
Equity securities: | Change in fair value
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	111	93
Equity securities: | Sales
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	10	0
Short-term investments
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	0	43
Cash equivalents
Gain (Loss) on Investments [Line Items]
Total net realized investment gains	$ 0	$ 146