Deferred Acquisition Costs and Value of Business Acquired (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
DAC
Balance at the beginning of the period	$ 467,845	$ 393,418	$ 353,408
Capitalized additions	105,814	93,222	63,093
Amortization and writedowns	(20,862)	(29,317)	(96,095)
Unrealized investment (gains) losses	(54,358)	10,522	73,012
Balance at the end of the period	498,439	467,845	393,418
VOBA
Balance at the beginning of the period	18,845	20,725	25,286
Amortization and writedowns	1,134	(1,992)	(4,493)
Unrealized investment (gains) losses	92	112	(68)
Balance at the end of the period	20,071	18,845	20,725
Total
Balance at the beginning of the period	518,510	486,690	414,143	$ 378,694
Capitalized additions	105,814	93,222	63,093
Amortization and writedowns	(19,728)	(31,309)	(100,588)
Unrealized investment (gains) losses	(54,266)	10,634	72,944
Balance at the end of the period	518,510	$ 486,690	$ 414,143	$ 378,694
Estimated future amortization of VOBA
Estimated future amortization of VOBA in 2018	3,800
Estimated future amortization of VOBA in 2019	3,800
Estimated future amortization of VOBA in 2020	3,800
Estimated future amortization of VOBA in 2021	3,800
Estimated future amortization of VOBA in 2022	$ 3,800