Commitments and Contingencies - Fair Value of Annuities (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	$ 100,074
Pacific Life and Annuity Company [Member] | A.M. Best Rating, A+ [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	18,028
American General Life Insurance Company [Member] | A.M. Best Rating, A [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	14,802
New York Life Insurance Company [Member] | A.M. Best Rating, A++ [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	10,335
Travelers Life and Annuity [Member] | A.M. Best Rating, A [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	12,414
Metropolitan Life Insurance Company [Member] | A.M. Best Rating, A+ [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	6,799
John Hancock Life Insurance Company [Member] | A.M. Best Rating, A+ [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	7,153
Athene Annuity and Life Company [Member] | A.M. Best Rating, A [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	4,638
United of Omaha Life Insurance Company [Member] | A.M. Best Rating, A+ [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	5,435
Other [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	$ 20,470