Accumulated Other Comprehensive Income - Components of AOCI (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
AOCI [Roll Forward]
Beginning Balance	$ 3,953,293	$ 3,703,829
OCI before reclassifications	(199,204)	26,385
Amounts reclassified from AOCI	(6,641)	19,771
Net current period OCI	(205,845)	46,156
Ending Balance	3,243,854	3,953,177
Unrealized gains (losses) on available-for-sale securities, net
AOCI [Roll Forward]
Beginning Balance	708,336	626,832
OCI before reclassifications	(199,204)	26,385
Amounts reclassified from AOCI	(6,641)	19,771
Net current period OCI	(205,845)	46,156
Ending Balance	502,491	672,988
Total Accumulated OCI Balance
AOCI [Roll Forward]
Beginning Balance	708,336	626,832
Ending Balance	$ 502,491	$ 672,988

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

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

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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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