Offsetting of Derivative Assets And Liabilities (Detail) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Assets
Gross estimated fair value of derivatives		$ 36,077	$ 39,022
Estimated fair value of derivatives presented on the Balance Sheets		8,212	16,526
Net amount after application of master netting agreements and collateral		129	1,304
Liabilities
Gross estimated fair value of derivatives		15,748	37,309
Estimated fair value of derivatives presented on the Balance Sheets		2,226	15,165
Net amount after application of master netting agreements and collateral		710	916
OTC - Bilateral
Assets
Gross estimated fair value of derivatives		34,487	37,344
Amounts offset on the balance sheets	[1]	(9,878)	(18,014)
Cash collateral	[2],[3]	(16,397)	(2,804)
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	[4]	(8,083)	(15,222)
Liabilities
Gross estimated fair value of derivatives		11,560	32,832
Amounts offset on the balance sheet	[1]	(9,878)	(18,014)
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	[4]	(1,516)	(14,249)
OTC - Cleared
Assets
Gross estimated fair value of derivatives		1,590	1,678
Amounts offset on the balance sheets	[1]	(1,590)	(1,678)
Liabilities
Gross estimated fair value of derivatives		4,188	4,477
Amounts offset on the balance sheet	[1]	(1,590)	(1,678)
Cash collateral	[2],[3]	$ (2,054)	$ (2,452)

[1] Estimated fair value of derivatives is limited to the amount that is subject to offset.

[2] The amount of cash collateral offset in the table above is limited to the net estimated fair value of derivatives after application of netting agreements. Cash collateral received for over-the-counter ("OTC") OTC-Bilateral and OTC-Cleared derivatives is included in cash and cash equivalents, short-term investments, or in fixed maturity securities, and the obligation to return it, beyond what is being offset, is included in payables for collateral under securities loaned, reverse repurchase agreements and derivatives. At December 31, 2017, the Company received excess cash collateral of $2,213. The Company had no excess cash collateral received from counterparties at December 31, 2016.

[3] The receivable for the return of cash collateral provided to the counterparty, beyond what is being offset, is included in other assets. At December 31, 2017 and 2016, the Company had no excess cash collateral provided to counterparties that was excluded from the table above due to the foregoing limitation. The amount reported in the table above does not include initial margin on Exchange-Traded and OTC-Cleared derivatives.

[4] Securities collateral received or pledged by the Company is held in separate custodial accounts and is not recorded on the Balance Sheets. The amount of securities collateral offset in the table above is limited to the net estimated fair value of derivatives after application of netting agreements and cash collateral. At December 31, 2017 and 2016, the Company received excess securities collateral with an estimated fair value of $4,214 and $395, respectively, for its OTC-bilateral derivatives, which are not included in the table above due to the foregoing limitation. At December 31, 2017 and 2016, the Company provided excess securities collateral with an estimated fair value of $146 and $1,878, respectively, for its OTC-Bilateral derivatives, which is not included in the table above due to the foregoing limitation. At December 31, 2017 and 2016, the Company also provided securities initial margin with an estimated fair value of $11,310 and $11,291, respectively, for its OTC-Cleared derivatives, which is not included in the table above.