Reinsurance - Reinsurance Recoverables and Financial Strength Ratings by Reinsurer (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Ceded Credit Risk [Line Items]
Reinsurance recoverables		$ 4,205,173	$ 4,193,562
Pecan Re Inc [Member] | External credit rating, not rated [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	[1],[2]	2,725,795	2,754,424
SCOR Global Life Reinsurance Companies [Member] | AM Best, A+ Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	[3]	354,458
SCOR Global Life Reinsurance Companies [Member] | AM Best, A Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables			355,759
Munich Re of Malta [Member] | External credit rating, not rated [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	[1],[4]	302,391	282,382
Swiss Re Life & Health America Inc. [Member] | AM Best, A+ Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	[5]	245,543	249,299
American Health and Life Insurance Company [Member] | AM Best, B Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables	[1]	172,956	176,010
Munich American Reassurance Company [Member] | AM Best, A+ Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables		112,841	106,471
Korean Reinsurance Company [Member] | AM Best, A Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables		102,915	96,921
RGA Reinsurance Company [Member] | AM Best, A+ Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables		90,037	84,473
Hannover Life Reassurance Company [Member] | AM Best, A+ Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables		32,250	22,929
TOA Reinsurance Company [Member] | AM Best, A+ Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables			23,977
TOA Reinsurance Company [Member] | AM Best, A Rating [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables		24,619
All Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverables		$ 41,368	$ 40,917

[1] Includes balances ceded under coinsurance transactions of term life insurance policies that were in force as of December 31, 2009. Amounts shown are net of their share of the reinsurance receivable from other reinsurers.

[2] Pecan Re Inc. is a wholly owned subsidiary of Swiss Re Life & Health America Inc.

[3] Includes amounts ceded to Transamerica Reinsurance Companies and fully retroceded to SCOR Global Life Reinsurance Companies.

[4] This entity, which is rated AA- by S&P, ultimately assumed FRAC's obligations under the 80% Canada Coinsurance Agreement as a result of the Munich Re Novation Agreement.

[5] Includes amounts ceded to Lincoln National Life Insurance and fully retroceded to Swiss Re Life & Health America Inc.