Inventory (Summary of Interests in Land Option Agreements) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Deposits and Pre-acquisition Costs	$ 244,568	$ 207,987
Remaining Purchase Price	2,738,855	2,462,579
Land options with VIEs
Variable Interest Entity [Line Items]
Deposits and Pre-acquisition Costs	85,173	78,889
Remaining Purchase Price	1,167,087	977,480
Other land options
Variable Interest Entity [Line Items]
Deposits and Pre-acquisition Costs	159,395	129,098
Remaining Purchase Price	$ 1,571,768	$ 1,485,099