Lease Agreements - Future minimum rental payments under operating and capital leases (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Capital leases minimum payments for 2016	$ 330
Capital leases minimum payments for 2017	95
Capital leases minimum payments for 2018	1
Capital leases minimum payments for 2019	0
Capital leases minimum payments for 2020	0
Capital leases minimum payments for later years	0
Capital leases minimum payments total	426
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating leases minimum payments for 2016	12,936
Operating leases minimum payments for 2017	11,313
Operating leases minimum payments for 2018	9,645
Operating leases minimum payments for 2019	8,056
Operating leases minimum payments for 2020	7,500
Operating leases minimum payments for later years	16,246
Operating leases minimum payments total	65,696
Built-to-suit Lease, Future Minimum Payments Due	19,097
Built-to-suit Lease, Future Minimum Payments Due, Next Twelve Months	687
Built-to-suit Lease, Future Minimum Payments Due in Two Years	1,156
Built-to-suit Lease, Future Minimum Payments Due in Three Years	1,180
Built-to-suit Lease, Future Minimum Payments Due in Four Years	1,203
Built-to-suit Lease, Future Minimum Payments Due in Five Years	1,227
Built-to-suit Lease, Future Minimum Payments Due Thereafter	$ 13,644