Available for Sale Debt Securities by Original Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
One year or less, amortized cost	$ 91,142	$ 27,752
Greater than one year and less than five years, amortized cost		5,705
Total available-for-sale debt securities, amortized cost	91,142	33,457
One year or less, fair value	91,137	27,727
Greater than one year and less than five years, fair value		5,699
Total available-for-sale debt securities fair value	$ 91,137	$ 33,426