Income Taxes - Principal Reasons for the Difference Between the Effective Tax Rate and UBT Statutory Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Amount [Abstract]
UBT statutory rate	$ 28,927	$ 25,244	$ 24,345
Corporate subsidiaries’ federal, state, local and foreign income taxes	17,907	31,223	30,353
Effect of ASC 740 adjustments, miscellaneous taxes, and other	(1,070)	2,965	3,393
Income not taxable resulting from use of UBT business apportionment factors	(17,445)	(14,635)	(13,787)
Income tax expense	$ 28,319	$ 44,797	$ 44,304
Effective Income Tax Rate Reconciliation, Percent [Abstract]
UBT statutory rate, percent	4.00%	4.00%	4.00%
Corporate subsidiaries’ federal, state, local and foreign income taxes, percent	2.50%	4.90%	5.00%
Effect of ASC 740 adjustments, miscellaneous taxes, and other, percent	(0.20%)	0.50%	0.60%
Income not taxable resulting from use of UBT business apportionment factors, percent	(2.40%)	(2.30%)	(2.30%)
Effective tax rate, percent	3.90%	7.10%	7.30%