Leases (Details 1) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Credit risk profile by creditworthiness category of direct financing lease receivables
Credit risk profile by creditworthiness category of direct financing lease receivables, Total	$ 497,103	$ 450,642
Very low risk to low risk
Credit risk profile by creditworthiness category of direct financing lease receivables
Credit risk profile by creditworthiness category of direct financing lease receivables, Total	201,434	192,853
Moderate
Credit risk profile by creditworthiness category of direct financing lease receivables
Credit risk profile by creditworthiness category of direct financing lease receivables, Total	198,464	194,234
Moderately high to high risk
Credit risk profile by creditworthiness category of direct financing lease receivables
Credit risk profile by creditworthiness category of direct financing lease receivables, Total	$ 97,205	$ 63,555