Summary of Change in Fair Value of Level 3 Fixed Maturity AFS Securities (Detail) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period		$ 57,381
Balance at end of period		41,169	$ 57,381
Fixed maturity AFS securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	[1]	9,215	6,666
Change in unrealized gains (losses)	[2]	222	(243)
Purchases		4,001	2,792
Sales		(2,189)	(326)
Transfers into Level 3		3,000	2,113
Transfers out of Level 3		(3,994)	(1,954)
Net realized investment gains	[3]	1	167
Balance at end of period	[1]	$ 10,256	$ 9,215

[1] Recorded as a component of fixed maturity AFS securities on the Balance Sheets.

[2] Recorded as a component of other comprehensive income (loss) (“OCI”) in net unrealized holding gains (losses) on AFS securities arising during the period.

[3] Recorded as a component of net realized investment gains (losses) on securities in the Statements of Income (Loss).