Fair Value Measurements - Contractual Maturities of Available For Sale Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Maturing in one year or less	$ 784	$ 973
Maturing in second year through fifth year	18,021	28,671
Maturing in sixth year through tenth year	24,076	21,651
Maturing after ten years	25,379	16,435
Total debt securities	$ 68,260	$ 67,730