Summary of Investments - SOI Securities Lending (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Securities Financing Transaction [Line Items]
Payable under securities lending agreements	$ 99,404	$ 0
U.S. government direct obligations and U.S. agencies
Securities Financing Transaction [Line Items]
Payable under securities lending agreements	6,220	0
Foreign government securities
Securities Financing Transaction [Line Items]
Payable under securities lending agreements	1,063	0
Corporate debt securities
Securities Financing Transaction [Line Items]
Payable under securities lending agreements	$ 92,121	$ 0