Investments - Cost and Fair Value of Debt Investments Based on Maturities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Available For Sale Securities Debt Maturities [Abstract]
Due in one year or less, Amortized Costs	$ 37,811	$ 32,536
Due within two years, Amortized Costs	41,166	49,558
Total, Amortized Costs	78,977	82,094
Due in one year or less, Fair Value	37,849	32,538
Due within two years, Fair Value	41,179	49,593
Total, Fair Value	$ 79,028	$ 82,131