Available for Sale Securities by Original Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, carrying value	$ 29,396	$ 30,700
Due greater than one year and less than three years, carrying value	2,031	6,134
Total cash equivalents and short-term investments, carrying value	31,427	36,834
Due in one year or less, fair value	29,389	30,701
Due greater than one year and less than three years, fair value	2,027	6,140
Total cash equivalents and short-term investments, fair value	$ 31,416	$ 36,841