Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Line Items]
Rent expense	$ 37,500	$ 34,000	$ 33,800
Investments, debt securities	12,983,213	13,605,963
Investments, equity securities	3,109,523	3,005,908
Stockholders' equity	$ 7,939,945	$ 7,554,707	$ 7,473,428	$ 6,923,757
Maximum
Commitments and Contingencies Disclosure [Line Items]
Non-cancelable operating leases, expiration date	2031
Energy Sector Business
Commitments and Contingencies Disclosure [Line Items]
Investments and equity in consolidated subsidiaries	$ 871,100
Investments, debt securities	313,300
Investments, equity securities	408,600
Energy Sector Business | Stranded Oil Resources Corporation
Commitments and Contingencies Disclosure [Line Items]
Stockholders' equity	$ 149,200