Commercial Mortgage Banking - Schedule of Amortization Expense (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Servicing Asset at Amortized Cost [Line Items]
2014	$ 1,023
2015	4,090
2016	4,083
2017	4,070
2018	4,030
Thereafter	12,200
Amortization expense	29,496	28,879	28,121	26,983
Originated MSRs [Member]
Servicing Asset at Amortized Cost [Line Items]
2014	704
2015	2,815
2016	2,808
2017	2,802
2018	2,775
Thereafter	9,071
Amortization expense	20,975
Purchased MSRs [Member]
Servicing Asset at Amortized Cost [Line Items]
2014	319
2015	1,275
2016	1,275
2017	1,268
2018	1,255
Thereafter	3,129
Amortization expense	$ 8,521