Segment Information - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Net income	$ 280,401		$ 275,344		$ 808,702	$ 788,697
Impact of Changes [Member]
Segment Reporting Information [Line Items]
Revenues		$ 6,000		$ 12,000
Net income		$ 3,000		$ 5,000
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Decrease in revenues			5,000			13,000
Decrease in net income			2,000			5,000
Net income	21,150		22,749		75,462	64,680
Residential Mortgage Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income			(2,272)			(7,464)
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Increase in revenues			5,000			13,000
Increase in net income			2,000			5,000
Net income	$ 85,312		78,676		$ 250,501	230,254
Commercial Real Estate [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income			$ 95			$ (414)