Accumulated Other Comprehensive Income - Components of AOCI (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI [Roll Forward]
Beginning Balance	$ 3,243,854	$ 3,953,177	$ 3,953,293	$ 3,703,829
OCI before reclassifications			(137,805)	85,218
Amounts reclassified from AOCI			(33,021)	27,040
Net current period OCI	35,019	66,102	(170,826)	112,258
Ending Balance	3,395,879	3,968,950	3,395,879	3,968,950
Unrealized gains (losses) on available-for-sale securities, net
AOCI [Roll Forward]
Beginning Balance			708,336	626,832
OCI before reclassifications			(137,805)	85,218
Amounts reclassified from AOCI			(33,021)	27,040
Net current period OCI			(170,826)	112,258
Ending Balance	537,510	739,090	537,510	739,090
Total Accumulated OCI Balance
AOCI [Roll Forward]
Beginning Balance	502,491	672,988	708,336	626,832
Net current period OCI	35,019	66,102	(170,826)	112,258
Ending Balance	$ 537,510	$ 739,090	$ 537,510	$ 739,090

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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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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