Senior Notes, Secured, and Unsecured Indebtedness - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 09, 2018	Mar. 08, 2018	Dec. 31, 2017	Mar. 31, 2017	Jan. 31, 2017	Dec. 31, 2016	Aug. 11, 2014	Mar. 31, 2014
ASSETS
Cash and cash equivalents	$ 50,473			$ 182,710	$ 39,508		$ 42,612
Receivables	14,018			10,223
Escrow proceeds receivable	1,552			3,319
Real estate inventories	2,051,817			1,699,850
Not owned	282,169			0
Investment in unconsolidated joint ventures	5,406			7,867
Goodwill	118,877			66,902
Intangibles, net	6,700			6,700
Deferred income taxes, net	47,716			47,915
Lease right-of-use assets	14,757			14,454
Other assets, net	32,921			21,164
Investments in subsidiaries	0			0
Intercompany receivables	0			0
Total assets	2,626,406			2,061,104
LIABILITIES AND EQUITY
Accounts payable	88,853			58,799
Accrued expenses	99,378			111,491
Liabilities from inventories not owned	282,169			0
Notes payable	172,246			94,515
Total debt	1,302,347			1,030,184
Intercompany payables	0			0
Total liabilities	1,772,747			1,200,474
Equity
William Lyon Homes stockholders’ equity (deficit)	782,285			780,472
Noncontrolling interests	71,374			80,158
Total liabilities and equity	2,626,406			2,061,104
5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	$ 0			$ 149,362
Equity
Stated interest rate	5.75%			5.75%
8 1/2% Senior Notes due November 15, 2020
Equity
Stated interest rate	8.50%			8.50%
7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	$ 346,924			$ 346,740
Equity
Stated interest rate	7.00%			7.00%
6% Senior Notes due 2023
LIABILITIES AND EQUITY
Total debt	$ 343,274			$ 0
Equity
Stated interest rate	6.00%
5 7/8% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Total debt	$ 439,903			439,567
Equity
Stated interest rate	5.875%
Guarantor Subsidiaries
ASSETS
Real estate inventories	$ 935,092
Not owned	282,169
LIABILITIES AND EQUITY
Liabilities from inventories not owned	282,169
Non-Guarantor Subsidiaries
ASSETS
Real estate inventories	233,623
Not owned	0
LIABILITIES AND EQUITY
Liabilities from inventories not owned	0
Delaware Lyon
ASSETS
Real estate inventories	0
Not owned	0
LIABILITIES AND EQUITY
Liabilities from inventories not owned	0
California Lyon
ASSETS
Real estate inventories	883,102
Not owned	0
LIABILITIES AND EQUITY
Liabilities from inventories not owned	0
Eliminations
ASSETS
Real estate inventories	0
Not owned	0
LIABILITIES AND EQUITY
Liabilities from inventories not owned	0
Reporting Entities | Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	3,576			156	430		272
Receivables	3,356			2,252
Escrow proceeds receivable	1,179			1,725
Real estate inventories				630,384
Investment in unconsolidated joint ventures	150			150
Goodwill	104,668			52,693
Intangibles, net	6,700			6,700
Deferred income taxes, net	0			0
Lease right-of-use assets	0			0
Other assets, net	10,682			2,504
Investments in subsidiaries	(837,268)			(494,201)
Intercompany receivables	285,102			269,831
Total assets	795,406			472,194
LIABILITIES AND EQUITY
Accounts payable	14,756			13,007
Accrued expenses	17,699			2,988
Notes payable	2,291			0
Intercompany payables	0			0
Total liabilities	316,915			15,995
Equity
William Lyon Homes stockholders’ equity (deficit)	478,491			456,199
Noncontrolling interests	0			0
Total liabilities and equity	795,406			472,194
Reporting Entities | Guarantor Subsidiaries | 5 3/4% Senior Notes due April 15, 2019
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 | 6% Senior Notes due 2023
LIABILITIES AND EQUITY
Total debt	0
Reporting Entities | Guarantor Subsidiaries | 5 7/8% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Total debt	0			0
Reporting Entities | Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	7,400			11,120	4,133		6,136
Receivables	3,252			3,324
Escrow proceeds receivable	0			0
Real estate inventories				238,459
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	467			493
Investments in subsidiaries	0			0
Intercompany receivables	0			0
Total assets	244,742			253,396
LIABILITIES AND EQUITY
Accounts payable	7,741			5,717
Accrued expenses	114			96
Notes payable	84,955			93,926
Intercompany payables	98,619			90,043
Total liabilities	191,429			189,782
Equity
William Lyon Homes stockholders’ equity (deficit)	(18,061)			(16,544)
Noncontrolling interests	71,374			80,158
Total liabilities and equity	244,742			253,396
Reporting Entities | Non-Guarantor Subsidiaries | 5 3/4% Senior Notes due April 15, 2019
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 | 6% Senior Notes due 2023
LIABILITIES AND EQUITY
Total debt	0
Reporting Entities | Non-Guarantor Subsidiaries | 5 7/8% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Total debt	0			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
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	782,285			780,472
Intercompany receivables	0			0
Total assets	782,285			780,472
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)	782,285			780,472
Noncontrolling interests	0			0
Total liabilities and equity	782,285			780,472
Reporting Entities | Delaware Lyon | 5 3/4% Senior Notes due April 15, 2019
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 | 6% Senior Notes due 2023
LIABILITIES AND EQUITY
Total debt	0
Reporting Entities | Delaware Lyon | 5 7/8% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Total debt	0			0
Reporting Entities | California Lyon
ASSETS
Cash and cash equivalents	39,497			171,434	34,945		36,204
Receivables	7,410			4,647
Escrow proceeds receivable	373			1,594
Real estate inventories				831,007
Investment in unconsolidated joint ventures	5,256			7,717
Goodwill	14,209			14,209
Intangibles, net	0			0
Deferred income taxes, net	47,716			47,915
Lease right-of-use assets	14,757			14,454
Other assets, net	21,772			18,167
Investments in subsidiaries	(18,061)			(16,544)
Intercompany receivables	0			0
Total assets	1,016,031			1,094,600
LIABILITIES AND EQUITY
Accounts payable	66,356			40,075
Accrued expenses	81,565			108,407
Notes payable	85,000			589
Intercompany payables	186,483			179,788
Total liabilities	1,549,505			1,264,528
Equity
William Lyon Homes stockholders’ equity (deficit)	(533,474)			(169,928)
Noncontrolling interests	0			0
Total liabilities and equity	1,016,031			1,094,600
Reporting Entities | California Lyon | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt				149,362
Reporting Entities | California Lyon | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	346,924			346,740
Reporting Entities | California Lyon | 6% Senior Notes due 2023
LIABILITIES AND EQUITY
Total debt	343,274
Reporting Entities | California Lyon | 5 7/8% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Total debt	439,903			439,567
Consolidation, Eliminations
ASSETS
Cash and cash equivalents	0			0	$ 0		$ 0
Receivables	0			0
Escrow proceeds receivable	0			0
Real estate inventories				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	73,044			(269,727)
Intercompany receivables	(285,102)			(269,831)
Total assets	(212,058)			(539,558)
LIABILITIES AND EQUITY
Accounts payable	0			0
Accrued expenses	0			0
Notes payable	0			0
Intercompany payables	(285,102)			(269,831)
Total liabilities	(285,102)			(269,831)
Equity
William Lyon Homes stockholders’ equity (deficit)	73,044			(269,727)
Noncontrolling interests	0			0
Total liabilities and equity	(212,058)			(539,558)
Consolidation, Eliminations | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt				0
Consolidation, Eliminations | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	0			0
Consolidation, Eliminations | 6% Senior Notes due 2023
LIABILITIES AND EQUITY
Total debt	0
Consolidation, Eliminations | 5 7/8% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Total debt	0			0
Senior Notes
LIABILITIES AND EQUITY
Total debt	1,130,101			935,669
Senior Notes | 5 3/4% Senior Notes due April 15, 2019
LIABILITIES AND EQUITY
Total debt	$ 0			$ 149,362
Equity
Stated interest rate	5.75%			5.75%					5.75%
Senior Notes | 8 1/2% Senior Notes due November 15, 2020
Equity
Stated interest rate	6.00%
Senior Notes | 7% Senior Notes due August 15, 2022
LIABILITIES AND EQUITY
Total debt	$ 346,924			$ 346,740
Equity
Stated interest rate	7.00%			7.00%				7.00%
Senior Notes | 6% Senior Notes due 2023
LIABILITIES AND EQUITY
Total debt	$ 343,274			$ 0
Equity
Stated interest rate		6.00%	6.00%		8.50%
Senior Notes | 5 7/8% Senior Notes due January 31, 2025
LIABILITIES AND EQUITY
Total debt	$ 439,903			$ 439,567
Equity
Stated interest rate	5.875%					5.875%