Cash, Cash Equivalents and Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents	$ 139,262	$ 82,387	$ 84,155	$ 61,653