Quarterly Results (unaudited) - Quarterly Financial Data and Operating Information (Detail) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($) Backlog Settlements order $ / shares	Sep. 30, 2020 USD ($) Backlog Settlements order $ / shares	Jun. 30, 2020 USD ($) Backlog Settlements order $ / shares	Mar. 31, 2020 USD ($) Backlog Settlements order $ / shares	Dec. 31, 2019 USD ($) Backlog Settlements order $ / shares	Sep. 30, 2019 USD ($) order Backlog Settlements $ / shares	Jun. 30, 2019 USD ($) order Backlog Settlements $ / shares	Mar. 31, 2019 USD ($) order Backlog Settlements $ / shares	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares
Quarterly Financial Information [Line Items]
Mortgage banking fees									$ 7,536,923	$ 7,388,664	$ 7,163,674
Net income	$ 305,004	$ 256,466	$ 164,075	$ 175,703	$ 256,137	$ 223,787	$ 210,209	$ 188,406	$ 901,248	$ 878,539	$ 797,197
Diluted earnings per share (USD per share) | $ / shares	$ 76.93	$ 65.11	$ 42.50	$ 44.96	$ 64.41	$ 56.11	$ 53.09	$ 47.64	$ 230.11	$ 221.13	$ 194.80
New orders (units) | order	5,485	6,681	5,901	5,015	4,392	4,766	5,239	5,139
Settlements (units) | Settlements	6,060	5,180	4,296	4,230	5,331	5,124	4,720	4,493
Backlog (units) | Backlog	11,549	12,124	10,623	9,018	8,233	9,172	9,530	9,011
Loans closed	$ 1,659,219	$ 1,382,060	$ 1,144,428	$ 1,132,104	$ 1,418,742	$ 1,373,946	$ 1,231,039	$ 1,140,999
Home Building
Quarterly Financial Information [Line Items]
Gross profit	441,552	384,707	304,265	260,964	379,467	355,055	332,060	304,400
Mortgage banking fees	2,263,673	1,920,751	1,588,758	1,555,707	1,946,859	1,873,331	1,757,448	1,643,206	$ 7,328,889	$ 7,220,844	$ 7,004,304
Mortgage Banking
Quarterly Financial Information [Line Items]
Mortgage banking fees	$ 80,342	$ 69,261	$ 31,610	$ 26,821	$ 43,336	$ 37,933	$ 42,746	$ 43,805	$ 208,034	$ 167,820	$ 159,370