Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018 USD ($) state region	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2018 USD ($) state region segment	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Segment Reporting [Abstract]
Number of states with active operations | state	13								13
Number of regions in which entity operates | region	3								3
Number of homebuilding segments | segment									3
Segment Reporting Information [Line Items]
Revenue	$ 767,945	$ 511,521	$ 455,178	$ 372,489	$ 672,981	$ 478,588	$ 425,468	$ 339,241	$ 2,107,133	$ 1,916,278	$ 1,822,114
Operating income	43,462	$ 17,580	$ 13,825	$ 6,681	37,783	$ 15,569	$ 7,511	$ 1,275	81,548	62,138	59,325
Depreciation and amortization									13,807	14,009	13,794
Write-off of a deposit on a legacy land investment									0	2,700	0
Excess insurance recovery											3,600
Reduction in home construction expenses									200	4,800
Capital Expenditures									17,020	12,440	12,219
Total Capital Expenditure, cash and noncash									17,020	12,440	12,219
Assets	2,128,102				2,220,995				2,128,102	2,220,995
Operating Segments
Segment Reporting Information [Line Items]
Operating income									245,632	222,696	191,290
Depreciation and amortization									12,734	12,698	11,710
Corporate and unallocated
Segment Reporting Information [Line Items]
Operating income									(164,084)	(160,558)	(131,965)
Depreciation and amortization									1,073	1,311	2,084
Capital Expenditures									3,522	341	461
Assets	542,713				810,881				542,713	810,881
West
Segment Reporting Information [Line Items]
Revenue									1,014,803	853,230	827,907
West | Operating Segments
Segment Reporting Information [Line Items]
Operating income									142,310	110,600	99,835
Depreciation and amortization									7,062	7,207	6,086
Capital Expenditures									8,152	7,086	6,570
Assets	835,230				779,964				835,230	779,964
East
Segment Reporting Information [Line Items]
Revenue									524,563	551,422	526,949
East | Operating Segments
Segment Reporting Information [Line Items]
Operating income									57,372	58,191	42,205
Depreciation and amortization									2,619	2,927	3,173
Capital Expenditures									2,234	2,474	2,441
Assets	335,474				298,532				335,474	298,532
Southeast
Segment Reporting Information [Line Items]
Revenue									567,767	511,626	467,258
Southeast | Operating Segments
Segment Reporting Information [Line Items]
Operating income									45,950	53,905	49,250
Depreciation and amortization									3,053	2,564	2,451
Capital Expenditures									3,112	2,539	$ 2,747
Assets	$ 414,685				$ 331,618				$ 414,685	$ 331,618