Fair Value - Changes in Level 3 assets (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Changes in Level 3 assets and liabilities measured at fair value on a recurring basis
Balance at the beginning of the period	$ 4,997	$ 0
Transfers to Level 3		4,997
Total gains or losses (realized/unrealized):
Changes in net assets	(656)	(656)
Balance at the end of the period	$ 4,341	$ 4,341
Significant Unobservable Inputs (Level 3)
Total gains or losses (realized/unrealized):
Financial assets having unobservable inputs classified as Level 3			$ 0
Financial liabilities having unobservable inputs classified as Level 3			$ 0