Goodwill and Acquired Intangible Assets - Gross Carrying Amount and Accumulated Amortization of Intangible Asset (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Beginning of year	$ 718	$ 1,501	$ 2,289
Acquired CDI	7,769	0	0
Amortization expense	(1,033)	(783)	(788)
End of year	$ 7,454	$ 718	$ 1,501