Contractual Maturities of Available-for-Sale Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013
Schedule of Available-for-sale Securities
Due within one year, cost	$ 586,818
Due after 1 year through 5 years, cost	231,188
Due after 5 years through 10 years, cost	3,924
Due after 10 years, cost	23,393
Total, cost	845,323
Due within one year, fair value	586,882
Due after 1 year through 5 years, fair value	231,201
Due after 5 years through 10 years, fair value	3,941
Due after 10 years, fair value	22,780
Total, fair value	$ 844,804