Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Line Items]
Rent expense	$ 40,000	$ 38,800	$ 37,000
Investments, debt securities	14,211,745	11,823,968
Investments, equity securities	2,505,496	3,572,790
Stockholders' equity	8,776,734	$ 7,692,710	$ 8,514,063	$ 7,939,945
Energy Sector Business
Commitments and Contingencies Disclosure [Line Items]
Investments and equity in consolidated subsidiaries	530,900
Investments, debt securities	329,200
Investments, equity securities	115,000
Energy Sector Business | Stranded Oil Resources Corporation
Commitments and Contingencies Disclosure [Line Items]
Stockholders' equity	$ 86,700
Maximum
Commitments and Contingencies Disclosure [Line Items]
Non-cancelable operating leases, expiration date	2038