Available-for-Sale Debt Securities by Original Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
One year or less, amortized cost	$ 66,291	$ 85,049
Marketable equity securities	0	0
Greater than one year and less than five years, amortized cost	10,111
Amortized Cost	76,402	85,049
One year or less, fair value	66,311	85,000
Marketable equity securities	4,487	11,163
Greater than one year and less than five years, fair value	10,144
Total available-for-sale securities fair value	$ 80,942	$ 96,163