Fair Value Measurements - Summary of Changes in Fair Value on Available-for-Sale Securities Measured at Fair Value on Recurring Basis using Significant Unobservable Inputs or Level 3 Inputs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Balance at beginning of period	$ 4,549	$ 4,856	$ 4,549	$ 4,856
Impairment of equity securities	(945)		(945)
Capital distribution		(307)		(307)
Balance at end of period	$ 3,604	$ 4,549	$ 3,604	$ 4,549