Cash, Cash Equivalents and Available-for-sale Securities (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents	$ 84,155,000	$ 61,653,000	$ 78,718,000	$ 146,470,000
Available-for-sale securities	$ 0	$ 50,097,000