Commercial Mortgage Banking - Summary of Changes in Carrying Value of Mortgage Servicing Rights (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Balance at beginning of year	$ 28,879		$ 26,983
Originations	5,956	[1]	7,351	[1]
Purchases	345		1,344
Disposals	(2,221)	[1]	(4,918)	[1]
Amortization expense	(2,819)		(1,881)
Balance at end of year	$ 30,140		$ 28,879

[1] Includes refinancings