Accumulated Other Comprehensive Income - Components of AOCI (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
AOCI [Roll Forward]
Beginning Balance	$ 3,123,533	$ 2,946,188
OCI before reclassifications	24,218	(88,527)
Amounts reclassified from AOCI	54,578	32,842
Net current period OCI	78,796	(55,685)
Ending Balance	3,634,977	3,123,533
Unrealized gains (losses) on available-for-sale securities, net
AOCI [Roll Forward]
Beginning Balance	718,106	773,791
OCI before reclassifications	24,218	(88,527)
Amounts reclassified from AOCI	54,578	32,842
Net current period OCI	78,796	(55,685)
Ending Balance	796,902	718,106
Total Accumulated OCI Balance
AOCI [Roll Forward]
Beginning Balance	718,106	773,791
Ending Balance	$ 796,902	$ 718,106

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

+ References

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-Publisher FASB
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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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