Senior Notes, Secured, and Unsecured Indebtedness - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 09, 2018	Mar. 08, 2018	Dec. 31, 2017	Jan. 31, 2017	Aug. 11, 2014
ASSETS
Cash and cash equivalents	$ 42,118	$ 33,779	$ 50,782			$ 182,710
Receivables	12,569	13,502
Escrow proceeds receivable	2,764	0
Real estate inventories - owned	2,327,582	2,333,207
Real estate inventories - not owned	215,541	315,576
Investment in unconsolidated joint ventures	1,552	5,542
Goodwill	123,695	123,695
Intangibles, net	6,700	6,700
Deferred income taxes	46,254	47,241
Lease right-of-use assets	37,000	13,561
Financial services assets	168,093	0
Other assets	35,136	36,971
Investments in subsidiaries	0	0
Intercompany receivables	0	0
Total assets	3,019,004	2,929,774
LIABILITIES AND EQUITY
Accounts payable	114,810	128,371
Accrued expenses	102,263	150,155
Financial services liabilities	146,836	0
Liabilities from inventories not owned	215,541	315,576
Notes payable	288,981	198,019
Senior notes	1,407,191	1,321,345
Intercompany payables	0	0
Total liabilities	1,986,641	1,915,447
Equity
William Lyon Homes stockholders’ equity	895,965	863,322
Noncontrolling interests	136,398	151,005
Total liabilities and equity	3,019,004	2,929,774
Senior notes
LIABILITIES AND EQUITY
Senior notes	1,118,210	1,123,326
7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Senior notes	$ 49,762	$ 347,456
Equity
Stated interest rate	7.00%	7.00%
7% Senior Notes due August 15, 2022 | Senior notes
LIABILITIES AND EQUITY
Senior notes	$ 49,762	$ 347,456
Equity
Stated interest rate	7.00%	7.00%						7.00%
6% Senior Notes due September 1, 2023
LIABILITIES AND EQUITY
Senior notes	$ 344,654	$ 343,878
Equity
Stated interest rate	6.00%	6.00%
6% Senior Notes due September 1, 2023 | Senior notes
LIABILITIES AND EQUITY
Senior notes	$ 344,654	$ 343,878
Equity
Stated interest rate	6.00%	6.00%		6.00%	6.00%
5.875% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Senior notes	$ 429,121	$ 431,992
Equity
Stated interest rate	5.875%	5.875%
5.875% Senior Notes due January 31, 2025 | Senior notes
LIABILITIES AND EQUITY
Senior notes	$ 429,121	$ 431,992
Equity
Stated interest rate	5.875%	5.875%					5.875%
6.625% Senior Notes Due 2027
LIABILITIES AND EQUITY
Senior notes	$ 294,673	$ 0
Equity
Stated interest rate	6.625%	6.625%	6.625%
6.625% Senior Notes Due 2027 | Senior notes
LIABILITIES AND EQUITY
Senior notes	$ 294,673	$ 0
Equity
Stated interest rate	6.625%			6.625%
Reporting Entities | Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	$ 2,562	2,888	$ 924			156
Receivables	2,392	4,151
Escrow proceeds receivable	0
Real estate inventories - owned	1,157,784	1,152,786
Real estate inventories - not owned	124,938	200,717
Investment in unconsolidated joint ventures	0	150
Goodwill	109,486	109,486
Intangibles, net	6,700	6,700
Deferred income taxes	0	0
Lease right-of-use assets	0	0
Financial services assets	0
Other assets	9,301	9,688
Investments in subsidiaries	(955,693)	(961,950)
Intercompany receivables	300,196	285,675
Total assets	757,666	810,291
LIABILITIES AND EQUITY
Accounts payable	34,393	34,546
Accrued expenses	8,775	26,967
Financial services liabilities	0
Liabilities from inventories not owned	124,938	200,717
Notes payable	1,252	1,231
Intercompany payables	0	0
Total liabilities	169,358	263,461
Equity
William Lyon Homes stockholders’ equity	588,308	546,830
Noncontrolling interests	0	0
Total liabilities and equity	757,666	810,291
Reporting Entities | Guarantor Subsidiaries | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Guarantor Subsidiaries | 6% Senior Notes due September 1, 2023
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Guarantor Subsidiaries | 5.875% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Guarantor Subsidiaries | 6.625% Senior Notes Due 2027
LIABILITIES AND EQUITY
Senior notes	0
Reporting Entities | Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	17,418	9,441	13,769			11,120
Receivables	5,106	3,297
Escrow proceeds receivable	0
Real estate inventories - owned	418,065	434,671
Real estate inventories - not owned	0	0
Investment in unconsolidated joint ventures	0	0
Goodwill	0	0
Intangibles, net	0	0
Deferred income taxes	0	0
Lease right-of-use assets	18,717	0
Financial services assets	168,093
Other assets	2,037	486
Investments in subsidiaries	0	0
Intercompany receivables	(21,508)	0
Total assets	607,928	447,895
LIABILITIES AND EQUITY
Accounts payable	34,436	15,363
Accrued expenses	103	100
Financial services liabilities	146,836
Liabilities from inventories not owned	0	0
Notes payable	137,729	151,788
Intercompany payables	123,567	113,580
Total liabilities	442,671	280,831
Equity
William Lyon Homes stockholders’ equity	28,859	16,059
Noncontrolling interests	136,398	151,005
Total liabilities and equity	607,928	447,895
Reporting Entities | Non-Guarantor Subsidiaries | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Non-Guarantor Subsidiaries | 6% Senior Notes due September 1, 2023
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Non-Guarantor Subsidiaries | 5.875% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Non-Guarantor Subsidiaries | 6.625% Senior Notes Due 2027
LIABILITIES AND EQUITY
Senior notes	0
Reporting Entities | Delaware Lyon
ASSETS
Cash and cash equivalents	0	0	0			0
Receivables	0	0
Escrow proceeds receivable	0
Real estate inventories - owned	0	0
Real estate inventories - not owned	0	0
Investment in unconsolidated joint ventures	0	0
Goodwill	0	0
Intangibles, net	0	0
Deferred income taxes	0	0
Lease right-of-use assets	0	0
Financial services assets	0
Other assets	0	0
Investments in subsidiaries	895,965	863,322
Intercompany receivables	0	0
Total assets	895,965	863,322
LIABILITIES AND EQUITY
Accounts payable	0	0
Accrued expenses	0	0
Financial services liabilities	0
Liabilities from inventories not owned	0	0
Notes payable	0	0
Intercompany payables	0	0
Total liabilities	0	0
Equity
William Lyon Homes stockholders’ equity	895,965	863,322
Noncontrolling interests	0	0
Total liabilities and equity	895,965	863,322
Reporting Entities | Delaware Lyon | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Delaware Lyon | 6% Senior Notes due September 1, 2023
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Delaware Lyon | 5.875% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Senior notes	0	0
Reporting Entities | Delaware Lyon | 6.625% Senior Notes Due 2027
LIABILITIES AND EQUITY
Senior notes	0
Reporting Entities | California Lyon
ASSETS
Cash and cash equivalents	22,138	21,450	36,089			171,434
Receivables	5,071	6,054
Escrow proceeds receivable	2,764
Real estate inventories - owned	751,733	745,750
Real estate inventories - not owned	90,603	114,859
Investment in unconsolidated joint ventures	1,552	5,392
Goodwill	14,209	14,209
Intangibles, net	0	0
Deferred income taxes	46,254	47,241
Lease right-of-use assets	18,283	13,561
Financial services assets	0
Other assets	23,798	26,797
Investments in subsidiaries	28,859	16,059
Intercompany receivables	0	0
Total assets	1,005,264	1,011,372
LIABILITIES AND EQUITY
Accounts payable	45,981	78,462
Accrued expenses	93,385	123,088
Financial services liabilities	0
Liabilities from inventories not owned	90,603	114,859
Notes payable	150,000	45,000
Intercompany payables	155,121	172,095
Total liabilities	1,653,300	1,656,830
Equity
William Lyon Homes stockholders’ equity	(648,036)	(645,458)
Noncontrolling interests	0	0
Total liabilities and equity	1,005,264	1,011,372
Reporting Entities | California Lyon | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Senior notes	49,762	347,456
Reporting Entities | California Lyon | 6% Senior Notes due September 1, 2023
LIABILITIES AND EQUITY
Senior notes	344,654	343,878
Reporting Entities | California Lyon | 5.875% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Senior notes	429,121	431,992
Reporting Entities | California Lyon | 6.625% Senior Notes Due 2027
LIABILITIES AND EQUITY
Senior notes	294,673
Eliminating Entries
ASSETS
Cash and cash equivalents	0	0	$ 0			$ 0
Receivables	0	0
Escrow proceeds receivable	0
Real estate inventories - owned	0	0
Real estate inventories - not owned	0	0
Investment in unconsolidated joint ventures	0	0
Goodwill	0	0
Intangibles, net	0	0
Deferred income taxes	0	0
Lease right-of-use assets	0	0
Financial services assets	0
Other assets	0	0
Investments in subsidiaries	30,869	82,569
Intercompany receivables	(278,688)	(285,675)
Total assets	(247,819)	(203,106)
LIABILITIES AND EQUITY
Accounts payable	0	0
Accrued expenses	0	0
Financial services liabilities	0
Liabilities from inventories not owned	0	0
Notes payable	0	0
Intercompany payables	(278,688)	(285,675)
Total liabilities	(278,688)	(285,675)
Equity
William Lyon Homes stockholders’ equity	30,869	82,569
Noncontrolling interests	0	0
Total liabilities and equity	(247,819)	(203,106)
Eliminating Entries | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Senior notes	0	0
Eliminating Entries | 6% Senior Notes due September 1, 2023
LIABILITIES AND EQUITY
Senior notes	0	0
Eliminating Entries | 5.875% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Senior notes	0	$ 0
Eliminating Entries | 6.625% Senior Notes Due 2027
LIABILITIES AND EQUITY
Senior notes	$ 0