Commitments and Contingencies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) entities	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Guaranteed Repayment of Economic Development Bonds	$ 30,000
Number of unconsolidated subsidiaries for which loans guaranteed | entities	2
Maximum Guarantee Exposure for Joint Venture Loans	$ 108,500
Total obligation for operating leases for certain land positions	34,400
Other Liabilities	210,825	$ 153,846
Special Tax Assessment [Member]
Loss Contingencies [Line Items]
Other Liabilities	10,700
Land [Member]
Loss Contingencies [Line Items]
Total obligation for operating leases for certain land positions	$ 93,300