Summary of Changes in Fair Value of Level 3 Liabilities (Assets) (Detail) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, balance at beginning of period		$ 55,143
Liabilities, balance at end of period		49,489	$ 55,143
Assets, Balance at beginning of period		(57,381)
Assets, balance at end of period		(46,237)	(57,381)
GMWB
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, balance at beginning of period	[1]	54,414	60,618
Liabilities, balance at end of period	[1]	48,760	54,414
GMWB | Interest rates
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, gain (loss) included in earnings	[2]	5,642	(4,179)
GMWB | Equity markets
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, gain (loss) included in earnings	[2]	(11,279)	(5,988)
GMWB | Other
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, gain (loss) included in earnings	[2]	(17)	3,963
GMIB
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Balance at beginning of period	[1]	(48,166)	(61,426)
Assets, balance at end of period	[1]	(36,890)	(48,166)
GMIB | Interest rates
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, gain (loss) included in earnings	[2]	(2,904)	2,262
GMIB | Equity markets
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, gain (loss) included in earnings	[2]	13,710	12,560
GMIB | Other
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, gain (loss) included in earnings	[2]	470	(1,562)
SALB
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, balance at beginning of period	[1]	729	511
Liabilities, balance at end of period	[1]	$ 729	729
SALB | Equity markets
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Liabilities, gain (loss) included in earnings	[2]		$ 218

[1] GMWB and SALB are recorded as a component of future policy benefits on the Balance Sheets and GMIB reinsurance is recorded as recoverable of ceded GMIB embedded derivatives, at fair value on the Balance Sheets.

[2] Recorded as a component of policy benefits in the Statements of Income (Loss).