Organization and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2017
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of ownership interest sold					100.00%
Impairment of goodwill and indefinite lived intangible assets		$ 0	$ 0	$ 0
Goodwill and other intangible assets		6,596,000	$ 6,451,000
Changes in the carrying value of the goodwill and indefinite lived intangible assets		$ 100,000
Corporate income tax rate		35.00%	35.00%	35.00%
Total future minimum lease payments		$ 91,204,000
Scenario Forecast
Organization And Summary Of Significant Accounting Policies [Line Items]
Corporate income tax rate	21.00%
Pro Forma
Organization And Summary Of Significant Accounting Policies [Line Items]
Cumulative-effect adjustment to net unrealized gains in accumulated other comprehensive income for available-for-sale equity securities		$ 11,800,000
Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life		3 years
Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life		7 years
Leasehold Improvements | Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life		5 years
Leasehold Improvements | Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life		10 years
Syndicate 1221
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage control of stamp capacity		100.00%