Debt (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Disclosure [Abstract]
Maximum amount borrowed	$ 412,000	$ 308,500	$ 270,600
Weighted average interest rate	1.94%	1.64%	1.69%