Capitalized Servicing Assets - Changes in Capitalized Servicing Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Residential Mortgage Loans [Member]
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	$ 120,509	$ 114,978	$ 117,351
Originations	26,067	28,985	28,792
Purchases	144,326	454	699
Amortization	(46,491)	(23,908)	(31,864)
Amortized value, ending balance	244,411	120,509	114,978
Valuation allowance	(7,000)
Ending balance, net	237,411	120,509	114,978
Commercial Mortgage Loans [Member]
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	114,663	114,076	103,764
Originations	41,370	26,298	34,620
Amortization	(25,397)	(25,711)	(24,308)
Amortized value, ending balance	130,636	114,663	114,076
Ending balance, net	$ 130,636	$ 114,663	$ 114,076