Reclassifications from Accumulated Other Comprehensive Income (Loss) to Condensed Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	$ 1,115,539	$ 975,526	$ 1,144,923	$ 1,021,944
Interest income and other, net	1,579	2,709	5,908	5,495
Tax effect	15,071	1,278	26,443	10,396
Total gains for the period, net of tax	(44,200)	(30,896)	(81,890)	(81,008)
Balance	1,077,764	943,908	1,077,764	943,908
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Balance	2,194	(403)	2,194	(147)
Losses recognized in OCI				(660)
Net period OCI				(256)
Total gains for the period, net of tax		0		(256)
Balance	$ 2,194	$ (403)	$ 2,194	(403)
Reclassification out of Accumulated Other Comprehensive Income \| Realized Gains on Available for Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income and other, net				$ 404

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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