Fair Value Measurements - Reconciliation for Investments Measured At Fair Value on Recurring Basis Level 3 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	$ 355,240	$ 270,903
Purchases	344,752	158,927
Sales	(139,962)	(104,684)
Total realized and unrealized gains (losses)	12,890	30,094
Net transfers into (out of) Level 3	191,536	0
Ending fair value	764,456	355,240
Fixed Maturity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	600	609
Purchases	0	0
Sales	(600)	0
Total realized and unrealized gains (losses)	0	(9)
Net transfers into (out of) Level 3	214,162	0
Ending fair value	214,162	600
Other Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	349,790	265,569
Purchases	344,752	158,927
Sales	(134,362)	(104,684)
Total realized and unrealized gains (losses)	12,740	29,978
Net transfers into (out of) Level 3	(22,626)	0
Ending fair value	550,294	349,790
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning fair value	4,850	4,725
Purchases	0	0
Sales	(5,000)	0
Total realized and unrealized gains (losses)	150	125
Net transfers into (out of) Level 3	0	0
Ending fair value	$ 0	$ 4,850