Goodwill and Acquired Intangible Assets - Gross Carrying Amount and Accumulated Amortization of Intangible Asset (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-lived Intangible Assets [Roll Forward]
Beginning of year	$ 18,937	$ 14,572	$ 8,594
Acquired CDI	10,170	7,726	8,464
Amortization expense	(4,300)	(3,361)	(2,486)
End of year	$ 24,807	$ 18,937	$ 14,572
Remaining average amortization period for CDI	58 months	63 months	64 months