Other Assets - Related party transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Assets [Abstract]
Revenues	$ 53,532	$ 30,517	$ 20,217
Expenses	$ 15,176	$ 12,795	$ 15,669