Fair Value Measurements - Reconciliation for Investments Measured At Fair Value on Recurring Basis Level 3 (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	$ 291,178	$ 47,717
Purchases	6,221	12,935
Sales	(28,761)	(14,224)
Total realized and unrealized gains (losses)	(10,717)	(2,343)
Net transfers into (out of) Level 3	(71,056)	0
Ending fair value	186,865	44,085
Fixed Maturity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	214,162	600
Purchases	0	0
Sales	(24,103)	(600)
Total realized and unrealized gains (losses)	(6,427)	0
Net transfers into (out of) Level 3	(71,056)	0
Ending fair value	112,576	0
Other Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	77,016	42,267
Purchases	6,221	12,935
Sales	(4,658)	(8,624)
Total realized and unrealized gains (losses)	(4,290)	(2,493)
Net transfers into (out of) Level 3	0	0
Ending fair value	74,289	44,085
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	0	4,850
Purchases	0	0
Sales	0	(5,000)
Total realized and unrealized gains (losses)	0	150
Net transfers into (out of) Level 3	0	0
Ending fair value	$ 0	$ 0