Senior Notes, Secured, and Unsecured Indebtedness - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jan. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Nov. 21, 2014	Aug. 11, 2014	Mar. 31, 2014	Nov. 08, 2012
ASSETS
Cash and cash equivalents	$ 43,604		$ 42,612	$ 40,710	$ 50,203
Receivables	9,719		9,538
Escrow proceeds receivable	228		85
Real estate inventories	1,855,658		1,771,998
Investment in unconsolidated joint ventures	8,225		7,282
Goodwill	66,902		66,902
Intangibles, net	6,700		6,700
Deferred income taxes, net	73,597		75,751
Lease right-of-use assets	15,074		13,129
Other assets, net	21,152		17,283
Investments in subsidiaries	0		0
Intercompany receivables	0		0
Total assets	2,100,859		2,011,280
LIABILITIES AND EQUITY
Accounts payable	84,116		74,282
Accrued expenses	93,140		92,919
Notes payable	161,011		155,768
Total debt	1,097,633		1,080,650
Intercompany payables	0		0
Total liabilities	1,274,889		1,247,851
Equity
William Lyon Homes stockholders’ equity (deficit)	735,984		697,086
Noncontrolling interests	89,986		66,343
Total liabilities and equity	2,100,859		2,011,280
Subordinated amortizing notes
LIABILITIES AND EQUITY
Total debt	1,619		7,225
Equity
Stated interest rate						5.50%
5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	$ 149,226		$ 148,826
Equity
Stated interest rate	5.75%		5.75%
8 1/2% Senior Notes due November 15, 2020
LIABILITIES AND EQUITY
Total debt	$ 0		$ 422,817
Equity
Stated interest rate	8.50%		8.50%
7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	$ 346,556		$ 346,014
Equity
Stated interest rate	7.00%		7.00%
Five Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Five [Member]
LIABILITIES AND EQUITY
Total debt	$ 439,221		$ 0
Equity
Stated interest rate	5.875%
Reporting Entities | Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	$ (328)		272	528	2,723
Receivables	1,760		3,303
Escrow proceeds receivable	0		0
Real estate inventories	697,824		645,341
Investment in unconsolidated joint ventures	150		150
Goodwill	52,693		52,693
Intangibles, net	6,700		6,700
Deferred income taxes, net	0		0
Lease right-of-use assets	0		0
Other assets, net	1,896		1,089
Investments in subsidiaries	(575,925)		(573,650)
Intercompany receivables	241,160		252,860
Total assets	425,930		388,758
LIABILITIES AND EQUITY
Accounts payable	25,061		16,416
Accrued expenses	4,719		4,636
Notes payable	0		2,979
Intercompany payables	0		0
Total liabilities	29,780		24,031
Equity
William Lyon Homes stockholders’ equity (deficit)	396,150		364,727
Noncontrolling interests	0		0
Total liabilities and equity	425,930		388,758
Reporting Entities | Guarantor Subsidiaries | Subordinated amortizing notes
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Guarantor Subsidiaries | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Guarantor Subsidiaries | 8 1/2% Senior Notes due November 15, 2020
LIABILITIES AND EQUITY
Total debt			0
Reporting Entities | Guarantor Subsidiaries | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Guarantor Subsidiaries | Five Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Five [Member]
LIABILITIES AND EQUITY
Total debt	0
Reporting Entities | Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	9,205		6,136	4,479	3,148
Receivables	3,911		3,246
Escrow proceeds receivable	0		0
Real estate inventories	257,444		216,063
Investment in unconsolidated joint ventures	0		0
Goodwill	0		0
Intangibles, net	0		0
Deferred income taxes, net	0		0
Lease right-of-use assets	0		0
Other assets, net	494		415
Investments in subsidiaries	0		0
Intercompany receivables	0		0
Total assets	271,054		225,860
LIABILITIES AND EQUITY
Accounts payable	10,605		5,486
Accrued expenses	103		98
Notes payable	105,785		102,076
Intercompany payables	82,822		75,593
Total liabilities	199,315		183,253
Equity
William Lyon Homes stockholders’ equity (deficit)	(18,249)		(23,736)
Noncontrolling interests	89,988		66,343
Total liabilities and equity	271,054		225,860
Reporting Entities | Non-Guarantor Subsidiaries | Subordinated amortizing notes
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Non-Guarantor Subsidiaries | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Non-Guarantor Subsidiaries | 8 1/2% Senior Notes due November 15, 2020
LIABILITIES AND EQUITY
Total debt			0
Reporting Entities | Non-Guarantor Subsidiaries | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Non-Guarantor Subsidiaries | Five Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Five [Member]
LIABILITIES AND EQUITY
Total debt	0
Reporting Entities | Delaware Lyon
ASSETS
Cash and cash equivalents	0		0	0	0
Receivables	0		0
Escrow proceeds receivable	0		0
Real estate inventories	0		0
Investment in unconsolidated joint ventures	0		0
Goodwill	0		0
Intangibles, net	0		0
Deferred income taxes, net	0		0
Lease right-of-use assets	0		0
Other assets, net	0		0
Investments in subsidiaries	735,984		697,086
Intercompany receivables	0		0
Total assets	735,984		697,086
LIABILITIES AND EQUITY
Accounts payable	0		0
Accrued expenses	0		0
Notes payable	0		0
Intercompany payables	0		0
Total liabilities	0		0
Equity
William Lyon Homes stockholders’ equity (deficit)	735,984		697,086
Noncontrolling interests	0		0
Total liabilities and equity	735,984		697,086
Reporting Entities | Delaware Lyon | Subordinated amortizing notes
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Delaware Lyon | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Delaware Lyon | 8 1/2% Senior Notes due November 15, 2020
LIABILITIES AND EQUITY
Total debt			0
Reporting Entities | Delaware Lyon | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	0		0
Reporting Entities | Delaware Lyon | Five Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Five [Member]
LIABILITIES AND EQUITY
Total debt	0
Reporting Entities | California Lyon
ASSETS
Cash and cash equivalents	34,727		36,204	35,703	44,332
Receivables	4,048		2,989
Escrow proceeds receivable	228		85
Real estate inventories	900,390		910,594
Investment in unconsolidated joint ventures	8,075		7,132
Goodwill	14,209		14,209
Intangibles, net	0		0
Deferred income taxes, net	73,597		75,751
Lease right-of-use assets	15,074		13,129
Other assets, net	18,762		15,779
Investments in subsidiaries	(18,249)		(23,736)
Intercompany receivables	0		0
Total assets	1,050,861		1,052,136
LIABILITIES AND EQUITY
Accounts payable	48,450		52,380
Accrued expenses	88,318		88,185
Notes payable	55,226		50,713
Intercompany payables	158,338		177,267
Total liabilities	1,286,954		1,293,427
Equity
William Lyon Homes stockholders’ equity (deficit)	(236,091)		(241,291)
Noncontrolling interests	(2)		0
Total liabilities and equity	1,050,861		1,052,136
Reporting Entities | California Lyon | Subordinated amortizing notes
LIABILITIES AND EQUITY
Total debt	1,619		7,225
Reporting Entities | California Lyon | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	149,226		148,826
Reporting Entities | California Lyon | 8 1/2% Senior Notes due November 15, 2020
LIABILITIES AND EQUITY
Total debt			422,817
Reporting Entities | California Lyon | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	346,556		346,014
Reporting Entities | California Lyon | Five Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Five [Member]
LIABILITIES AND EQUITY
Total debt	439,221
Consolidation, Eliminations
ASSETS
Cash and cash equivalents	0		0	$ 0	$ 0
Receivables	0		0
Escrow proceeds receivable	0		0
Real estate inventories	0		0
Investment in unconsolidated joint ventures	0		0
Goodwill	0		0
Intangibles, net	0		0
Deferred income taxes, net	0		0
Lease right-of-use assets	0		0
Other assets, net	0		0
Investments in subsidiaries	(141,810)		(99,700)
Intercompany receivables	(241,160)		(252,860)
Total assets	(382,970)		(352,560)
LIABILITIES AND EQUITY
Accounts payable	0		0
Accrued expenses	0		0
Notes payable	0		0
Intercompany payables	(241,160)		(252,860)
Total liabilities	(241,160)		(252,860)
Equity
William Lyon Homes stockholders’ equity (deficit)	(141,810)		(99,700)
Noncontrolling interests	0		0
Total liabilities and equity	(382,970)		(352,560)
Consolidation, Eliminations | Subordinated amortizing notes
LIABILITIES AND EQUITY
Total debt	0		0
Consolidation, Eliminations | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	0		0
Consolidation, Eliminations | 8 1/2% Senior Notes due November 15, 2020
LIABILITIES AND EQUITY
Total debt			0
Consolidation, Eliminations | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	0		0
Consolidation, Eliminations | Five Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Five [Member]
LIABILITIES AND EQUITY
Total debt	0
Senior Notes
LIABILITIES AND EQUITY
Total debt	935,003		917,657
Senior Notes | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	$ 149,226		$ 148,826
Equity
Stated interest rate	5.75%		5.75%					5.75%
Senior Notes | 8 1/2% Senior Notes due November 15, 2020
LIABILITIES AND EQUITY
Total debt	$ 0		$ 422,817
Equity
Stated interest rate	8.50%		8.50%						8.50%
Senior Notes | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	$ 346,556		$ 346,014
Equity
Stated interest rate	7.00%		7.00%				7.00%
Senior Notes | Five Point Eight Seven Five Percent Senior Notes Due Two Thousand Twenty Five [Member]
LIABILITIES AND EQUITY
Total debt	$ 439,221		$ 0
Equity
Stated interest rate	5.875%	5.875%