Difference Between Income Taxes Computed at Federal Statutory Rate and Provision for Income Taxes (Detail)	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	35.00%	28.10%	35.00%	35.00%
Effect of:
Foreign earnings taxed at lower rates			(7.80%)	(11.60%)	(14.50%)
Impacts of TCJA			37.70%	0.00%	0.00%
Phone business losses			0.00%	(5.70%)	1.00%
Excess tax benefits relating to stock-based compensation			(2.50%)	(2.10%)	(1.60%)
Interest, net			1.20%	1.40%	0.90%
Other reconciling items, net			(2.10%)	(2.20%)	(0.90%)
Effective rate			54.60%	14.80%	19.90%