Financial Instruments - Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Amortized cost
Maturing within one year, Amortized cost	$ 211,311	$ 78,649
Maturing in one to five years, Amortized cost	108,202	25,567
Total available-for-sale securities, Amortized cost	319,513	104,216
Estimated Fair value
Maturing within one year, Estimated fair value	211,059	78,611
Maturing in one to five years, Estimated fair value	107,935	25,505
Total available-for-sale securities, Estimated fair value	$ 318,994	$ 104,116