Fair Value of Financial Instruments (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Amortized Cost Basis
Amortized Cost	$ 35,356,000
Unrealized Losses	(24,000)	$ (37,000)
Estimated Fair Value	35,332,000
Level I
Assets:
Money market funds	98,000	16,376,000
Total assets measured at fair value	98,000	16,376,000
Level II
Assets:
Corporate bonds and commercial paper	23,656,000	43,304,000
Total assets measured at fair value	23,656,000	43,304,000
Fair Value, Measurements, Recurring Basis
Assets:
Money market funds	98,000	16,376,000
Corporate bonds and commercial paper	23,656,000	43,304,000
Total assets measured at fair value	23,754,000	$ 59,680,000
Cash
Available-for-sale Securities, Amortized Cost Basis
Amortized Cost	11,578,000
Estimated Fair Value	11,578,000
Money market funds
Available-for-sale Securities, Amortized Cost Basis
Amortized Cost	98,000
Estimated Fair Value	98,000
Corporate debt securities and commercial paper
Available-for-sale Securities, Amortized Cost Basis
Amortized Cost	23,680,000
Unrealized Losses	(24,000)
Estimated Fair Value	$ 23,656,000