Offsetting of Derivative Assets And Liabilities (Detail) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Assets
Gross estimated fair value of derivatives		$ 51,110	$ 36,077
Estimated fair value of derivatives presented on the Balance Sheets		5,352	8,212
Net amount after application of master netting agreements and collateral		263	129
Liabilities
Gross estimated fair value of derivatives		17,610	15,748
Estimated fair value of derivatives presented on the Balance Sheets		1,716	2,226
Net amount after application of master netting agreements and collateral		0	710
OTC - Bilateral
Assets
Gross estimated fair value of derivatives		48,057	34,487
Amounts offset on the balance sheets	[1]	(5,502)	(9,878)
Cash collateral	[2],[3]	(37,340)	(16,397)
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	[4]	(5,089)	(8,083)
Liabilities
Gross estimated fair value of derivatives		7,218	11,560
Amounts offset on the balance sheet	[1]	(5,502)	(9,878)
Gross Amounts Not Offset in the Balance Sheet, Financial Instruments	[4]	(1,716)	(1,516)
OTC - Cleared
Assets
Gross estimated fair value of derivatives		2,799	1,590
Amounts offset on the balance sheets	[1]	(2,799)	(1,590)
Liabilities
Gross estimated fair value of derivatives		10,274	4,188
Amounts offset on the balance sheet	[1]	(2,799)	(1,590)
Cash collateral	[2],[3]	(7,476)	$ (2,054)
Exchange-traded
Assets
Gross estimated fair value of derivatives		254
Amounts offset on the balance sheets	[1]	(117)
Liabilities
Gross estimated fair value of derivatives		118
Amounts offset on the balance sheet	[1]	$ (117)

[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 OTC-Bilateral and OTC-Cleared derivatives is included in cash and cash equivalents, short-term investments, or fixed maturity securities, and the obligation to return it, beyond what is already being offset, is included in payables for collateral under securities loaned, reverse repurchase agreements and derivatives. At March 31, 2018 and December 31, 2017,

[3] The receivable for the return of cash collateral provided to the counterparty, beyond what is being offset, is included in other assets. The amount reported in the table above does not include initial margin on exchange-traded and OTC-Cleared derivatives. At March 31, 2018, the Company provided excess cash collateral of $294. The Company had no excess cash collateral provided to counterparties at December 31, 2017.

[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 March 31, 2018 and December 31, 2017, the Company received excess securities collateral with an estimated fair value of $2,995 and $4,214, respectively, for its OTC-Bilateral derivatives, which are not included in the table above due to the foregoing limitation. At March 31, 2018 and December 31, 2017, the Company provided excess securities collateral with an estimated fair value of $1,052 and $146, respectively, for its OTC-Bilateral derivatives, which is not included in the table above due to the foregoing limitation. At March 31, 2018 and December 31, 2017, the Company also provided securities for initial margin with an estimated fair value of $10,846 and $11,310, respectively, for its OTC-Cleared derivatives, which is not included in the table above.