Commercial Mortgage Banking - Summary of Changes in Carrying Value of Mortgage Servicing Rights (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Transfers and Servicing [Abstract]
Balance at beginning of period	$ 28,879		$ 26,983
Originations	4,252	[1]	5,668	[1]
Purchases	144		1,108
Disposals	(1,754)	[1]	(4,518)	[1]
Amortization expense	(2,025)		(1,120)
Balance at end of period	$ 29,496		$ 28,121

[1] Includes refinancings