Capitalized Servicing Assets - Changes in Capitalized Servicing Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Residential Mortgage Loans [Member]
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	$ 114,978	$ 117,351	$ 118,303
Originations	28,985	28,792	28,618
Purchases	454	699	638
Amortization	(23,908)	(31,864)	(30,208)
Amortized value, ending balance	120,509	114,978	117,351
Ending balance, net	120,509	114,978	117,351
Commercial Mortgage Loans [Member]
Servicing Asset at Amortized Cost [Line Items]
Amortized value, Beginning balance	114,076	103,764	83,692
Originations	26,298	34,620	40,117
Amortization	(25,711)	(24,308)	(20,045)
Amortized value, ending balance	114,663	114,076	103,764
Ending balance, net	$ 114,663	$ 114,076	$ 103,764