Quarterly Results (unaudited) - Quarterly Financial Data and Operating Information (Detail) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) Settlements Backlog order $ / shares	Sep. 30, 2018 USD ($) Settlements Backlog order $ / shares	Jun. 30, 2018 USD ($) Settlements Backlog order $ / shares	Mar. 31, 2018 USD ($) Settlements Backlog order $ / shares	Dec. 31, 2017 USD ($) Settlements Backlog order $ / shares	Sep. 30, 2017 USD ($) Settlements Backlog order $ / shares	Jun. 30, 2017 USD ($) Settlements Backlog order $ / shares	Mar. 31, 2017 USD ($) Settlements Backlog order $ / shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares
Quarterly Financial Information [Line Items]
Mortgage banking fees									$ 7,163,674	$ 6,305,840	$ 5,822,544
Net income	$ 232,158	$ 195,816	$ 203,174	$ 166,049	$ 124,619	$ 162,102	$ 147,877	$ 102,923	$ 797,197	$ 537,521	$ 425,262
Diluted earnings per share (USD per share) | $ / shares	$ 58.57	$ 48.28	$ 49.05	$ 39.34	$ 28.88	$ 38.02	$ 35.19	$ 25.12	$ 194.80	$ 126.77	$ 103.61
New orders (units) | order	3,841	4,302	4,964	5,174	4,306	4,200	4,678	4,424
Settlements (units) | Settlements	5,186	4,754	4,611	3,896	4,630	4,158	3,917	3,256
Backlog, end of period (units) | Backlog	8,365	9,710	10,162	9,809	8,531	8,855	8,813	8,052
Loans closed	$ 1,356,430	$ 1,249,199	$ 1,214,101	$ 1,009,673	$ 1,229,695	$ 1,115,494	$ 1,041,613	$ 843,341
Homebuilding:
Quarterly Financial Information [Line Items]
Gross profit – homebuilding operations	363,668	336,696	333,666	278,147	343,187	325,755	294,631	221,570
Mortgage banking fees	1,954,403	1,809,345	1,750,463	1,490,093	1,781,494	1,633,726	1,512,714	1,247,587	$ 7,004,304	$ 6,175,521	$ 5,709,223
Mortgage Banking:
Quarterly Financial Information [Line Items]
Mortgage banking fees	$ 40,145	$ 43,062	$ 36,842	$ 39,321	$ 34,842	$ 34,194	$ 31,778	$ 29,505	$ 159,370	$ 130,319	$ 113,321