Investments - Schedule of Changes in Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 601,188	$ 575,946
Total gains or losses:
Included in realized gains/losses	788	1,182
Included in other comprehensive income	29,486	9,676
Acquisitions	33,662	38,600
Sales	0	0
Amortization	3,525	4,197
Other	(17,614)	(17,819)
Transfers in and/or out of Level 3	0	0
Ending balance	$ 651,035	$ 611,782
Percent of total fixed maturities	4.10%	4.30%
Collateralized debt obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 70,382	$ 63,232
Total gains or losses:
Included in realized gains/losses	0	0
Included in other comprehensive income	(3,879)	12,797
Acquisitions	0	0
Sales	0	0
Amortization	3,511	4,183
Other	(6,732)	(8,100)
Transfers in and/or out of Level 3	0	0
Ending balance	$ 63,282	$ 72,112
Percent of total fixed maturities	0.40%	0.50%
Corporates [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 530,806	$ 512,714
Total gains or losses:
Included in realized gains/losses	788	1,182
Included in other comprehensive income	33,365	(3,121)
Acquisitions	33,662	38,600
Sales	0	0
Amortization	14	14
Other	(10,882)	(9,719)
Transfers in and/or out of Level 3	0	0
Ending balance	$ 587,753	$ 539,670
Percent of total fixed maturities	3.70%	3.80%