Borrowings - Short-Term Credit Facilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-Term Credit Facilities
Interest expense	$ 28,327	$ 29,254	$ 30,894
Short-Term Credit Facilities
Short-Term Credit Facilities
Weighted average interest rate	3.12%	2.48%
Interest expense	$ 6,300	$ 5,500	$ 3,300