Commitments and Contingencies - Fair Value of Annuities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	$ 94,561
Metropolitan Life Insurance Company (A+) [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	15,451
American General Life Insurance (A) [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	15,432
Pacific Life and Annuity Company (A+) [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	15,306
New York Life Insurance Company (A++) [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	12,131
John Hancock Life Insurance Company USA (A+) [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	7,854
Athene Annuity and Life Assurance Company (B++) [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	6,543
Liberty Life Assurance Company of Boston (A) [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	4,020
Other [Member]
Commitments And Contingencies [Line Items]
Statement value of annuities exceeding 1% of statutory surplus	$ 17,824