Summary of Significant Accounting Policies (Narrative) (Details) $ in Thousands, shares in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Mar. 31, 2017 USD ($) home lot
Income statement impact ASU 2016-09 adoption		7700
Intangible asset useful life		20 years
Unfunded settlements		$ 80,300	$ 66,500
Restricted Cash and Cash Equivalents		33,485	24,366
Intangible assets, acquired cost (gross)		277,000	277,000
Intangible assets, accumulated amortization		176,400	162,600
Intangible assets amortization expense		13,800	13,800	$ 12,900
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months		13,800
Future Amortization Expense, Year Two		13,800
Future Amortization Expense, Year Three		13,800
Future Amortization Expense, Year Four		10,404
Future Amortization Expense, Year Five		5,650
Property and equipment, net		70,706	77,444
Property and equipment, accumulated depreciation		206,500	192,900
Depreciation Expense		37,200	40,200	33,300
Advertising Expense		45,000	50,700	45,300
Employee benefit plan company contributions		$ 15,700	$ 14,600	$ 12,600
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares		0.1	1.8	3.9
Number of VIEs requiring consolidation		0
Residential mortgage loans available-for-sale		$ 570,600	$ 539,496
Residential mortgage loans available-for-sale aggregate outstanding principal balance		553,500	529,700
Net gain (loss) from change in fair value		(2,200)	2,800
Net gains from the sale of mortgages		110,900	109,600	$ 80,800
Loans held for investment, net		$ 11,200	8,400
Days past contractual term once loans no longer accrue interest income		90 days
Variability in future cash flows of derivative instruments in days		60 days
Furniture and Fixtures [Member]
Property and equipment, useful life		2 years
Minimum [Member]
Period of Reimbursement of Payments on Loan Prepay in Days		90 days
Minimum [Member] | Equipment [Member]
Property and equipment, useful life		3 years
Maximum [Member]
Period of Reimbursement of Payments on Loan Prepay in Days		120 days
Maximum [Member] | Equipment [Member]
Property and equipment, useful life		10 years
Financial Services [Member]
Interest income on mortgage loans		$ 9,500	8,000	$ 6,900
Interest Rate Lock Commitments [Member]
Derivative, notional amount		210,900	273,900
Forward Contracts [Member]
Derivative, notional amount		522,000	610,000
Whole Loan Commitments [Member]
Derivative, notional amount		$ 203,100	157,600
JW Homes (Wieland) [Member] | JW Homes (Wieland) [Member]
Number of Units in Real Estate Property | lot					317
JW Homes (Wieland) [Member]
Business Combination, Consideration Transferred	$ 430,500
Number of Units in Real Estate Property | lot					7,000
Goodwill					$ 40,400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net					$ 18,000
JW Homes (Wieland) [Member] | JW Homes (Wieland) [Member]
Number of Units in Real Estate Property | home					375
JW Homes (Wieland) [Member] | Land Option Contracts [Member]
Number of Units in Real Estate Property | lot					1,300
Restricted stock [Member]
Share-based compensation vesting period		3 years
Accounting Standards Update 2016-09, Excess Tax Benefit Component [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ 18,600