Hierarchy of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015
Assets
Fixed maturity available-for-sale securities, at estimated fair value		$ 1,745,072	$ 1,665,337
Equity available-for-sale securities		33,827	34,667
Derivative assets		1,123	10,893
Limited partnerships		69,489	63,489
Fair value recoverable of ceded GMIB embedded derivatives		73,834	61,426
Separate Accounts assets		5,668,318	5,940,665
Liabilities
Derivative liabilities		2,470	13,075
Corporate securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value		1,022,552	1,016,792
Asset-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value		84,397	122,654
Commercial mortgage-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value		81,517	71,683
Residential mortgage-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value		161,539	59,265
Municipals
Assets
Fixed maturity available-for-sale securities, at estimated fair value		807	807
Government and government agencies - United States
Assets
Fixed maturity available-for-sale securities, at estimated fair value		386,018	386,288
Government and government agencies - Foreign
Assets
Fixed maturity available-for-sale securities, at estimated fair value		8,242	7,848
Banking securities
Assets
Equity available-for-sale securities		27,938	28,673
Industrial securities
Assets
Equity available-for-sale securities		5,889	5,994
Fair Value, Measurements, Recurring
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	1,745,072	1,665,337
Equity available-for-sale securities	[1]	33,827	34,667
Cash equivalents	[2]	330,702	234,500
Derivative assets	[3]	1,123	10,893
Limited partnerships	[4]	69,489	63,489
Fair value recoverable of ceded GMIB embedded derivatives	[5]	73,834	61,426
Separate Accounts assets	[6]	5,668,318	5,940,665
Total assets		7,922,365	8,010,977
Liabilities
Future policy benefits (embedded derivatives only)	[7]	85,001	61,129
Derivative liabilities	[3]	2,470	13,075
Total liabilities		87,471	74,204
Fair Value, Measurements, Recurring | Corporate securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	1,022,552	1,016,792
Fair Value, Measurements, Recurring | Asset-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	84,397	122,654
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	81,517	71,683
Fair Value, Measurements, Recurring | Residential mortgage-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	161,539	59,265
Fair Value, Measurements, Recurring | Municipals
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	807	807
Fair Value, Measurements, Recurring | Government and government agencies - United States
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	386,018	386,288
Fair Value, Measurements, Recurring | Government and government agencies - Foreign
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	8,242	7,848
Fair Value, Measurements, Recurring | Banking securities
Assets
Equity available-for-sale securities	[1]	27,938	28,673
Fair Value, Measurements, Recurring | Industrial securities
Assets
Equity available-for-sale securities	[1]	5,889	5,994
Level 1 | Fair Value, Measurements, Recurring
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	387,543	387,787
Separate Accounts assets	[6]	5,668,318	5,940,665
Total assets		6,055,861	6,328,452
Level 1 | Fair Value, Measurements, Recurring | Government and government agencies - United States
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	386,018	386,288
Level 1 | Fair Value, Measurements, Recurring | Government and government agencies - Foreign
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	1,525	1,499
Level 2 | Fair Value, Measurements, Recurring
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	1,350,769	1,270,884
Equity available-for-sale securities	[1]	33,827	34,667
Cash equivalents	[2]	330,702	234,500
Derivative assets	[3]	1,123	10,893
Limited partnerships	[4]	59,113	61,373
Total assets		1,775,534	1,612,317
Liabilities
Derivative liabilities	[3]	2,470	13,075
Total liabilities		2,470	13,075
Level 2 | Fair Value, Measurements, Recurring | Corporate securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	1,022,552	1,016,792
Level 2 | Fair Value, Measurements, Recurring | Asset-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	77,637	115,988
Level 2 | Fair Value, Measurements, Recurring | Commercial mortgage-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	81,517	71,683
Level 2 | Fair Value, Measurements, Recurring | Residential mortgage-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	161,539	59,265
Level 2 | Fair Value, Measurements, Recurring | Municipals
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	807	807
Level 2 | Fair Value, Measurements, Recurring | Government and government agencies - Foreign
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	6,717	6,349
Level 2 | Fair Value, Measurements, Recurring | Banking securities
Assets
Equity available-for-sale securities	[1]	27,938	28,673
Level 2 | Fair Value, Measurements, Recurring | Industrial securities
Assets
Equity available-for-sale securities	[1]	5,889	5,994
Level 3 | Fair Value, Measurements, Recurring
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	6,760	6,666
Limited partnerships	[4]	10,376	2,116
Fair value recoverable of ceded GMIB embedded derivatives	[5]	73,834	61,426
Total assets		90,970	70,208
Liabilities
Future policy benefits (embedded derivatives only)	[7]	85,001	61,129
Total liabilities		85,001	61,129
Level 3 | Fair Value, Measurements, Recurring | Asset-backed securities
Assets
Fixed maturity available-for-sale securities, at estimated fair value	[1]	$ 6,760	$ 6,666

[1] Securities are classified as Level 1 if the fair value is determined by observable inputs that reflect quoted prices for identical assets in active markets that the Company has the ability to access at the measurement date. Level 1 securities primarily include highly liquid U.S. Treasury and U.S. government agency securities. Securities are classified as Level 2 if the fair value is determined by observable inputs, other than quoted prices included in Level 1, for the asset or prices for similar assets. Securities are classified as Level 3 if the valuations are derived from techniques in which one or more of the significant inputs are unobservable. Level 3 consists principally of fixed maturity securities whose fair value is estimated based on non-binding broker quotes and internal models. These internal models primarily use projected cash flows discounted using relevant risk spreads and market interest rate curves. At June 30, 2016 and December 31, 2015, there were no fixed maturity AFS securities valued using internal models.

[2] Cash equivalents are primarily valued at amortized cost, which approximates fair value. Operating cash is not included in the above table.

[3] Level 2 derivatives include interest rate swaps, inflation swaps, variance swaps, total return swaps, and credit default swaps for which the Company utilized readily accessible quoted index levels and broker quotes. The fair value of interest rate swaps is calculated based on the change in the underlying floating rate curve (LIBOR) at the reporting date, as compared to the fixed leg of the swap. The fair value for inflation swaps is calculated as the difference between the consumer price index (or related readily accessible quoted inflation index level) at the reporting date from the last reset date, multiplied by the notional value of the swap. The fair value for the variance swaps is calculated as the difference between the estimated volatility of the underlying Standard and Poor's 500 Composite Stock Price Index ("S&P") at maturity to the actual volatility of the underlying S&P index at initiation (i.e., strike) multiplied by the notional value of the swap. Total return swaps are valued based on the change in the underlying equity index as of the last reset date. Credit default swaps are valued using a discounted cash flow model where future premium payments and protection payments are corrected for the probability of default which is modeled using an arbitrage free credit spread model.

[4] Limited partnership investments in which management is able to determine that observable market inputs have been used and can be redeemed at the net asset value in 90 days or less are considered Level 2. The Company has investments in two limited partnerships for which the fair values are derived from management's review of the financial information that is obtained from the private equity funds and prepared on a GAAP basis and are considered Level 3 measurements. The valuation input of these financial statements is on a one quarter lag.

[5] Guaranteed minimum income benefit ("GMIB") reinsurance is treated as embedded derivatives and is reported as a recoverable of ceded GMIB embedded derivatives, at fair value in the Balance Sheets.

[6] Separate Accounts assets are carried at the net asset value provided by the fund managers.

[7] The Company issued contracts containing guaranteed minimum withdrawal benefit riders ("GMWB") and obtained GMIB reinsurance. GMWB and GMIB reinsurance are treated as embedded derivatives and are required to be reported separately from the host contract. In addition, the Company issues SALB contracts which are required to be reported at fair value. The fair value of these guarantees is calculated as the present value of future expected payments to policyholders less the present value of assessed fees attributable to the guarantees. Given the complexity and long-term nature of these guarantees, their fair values are determined using stochastic techniques under a variety of market return, discount rates and actuarial assumptions. Since two of the assumptions are unobservable and are considered to be significant inputs to the liability valuation, the liability included in future policy benefits has been reflected within Level 3 of the fair value hierarchy.