Goodwill and Core Deposit Intangibles - CDI Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gross amount of CDI:
Balance, beginning of year	$ 54,809	$ 15,102	$ 10,782
Additions due to acquisitions	71,136	39,707	4,320
Balance, end of year	125,945	54,809	15,102
Accumulated amortization:
Balance, beginning of year	(11,795)	(5,651)	(3,612)
Amortization	(13,594)	(6,144)	(2,039)
Balance, end of year	(25,389)	(11,795)	(5,651)
Net CDI, end of year	$ 100,556	$ 43,014	$ 9,451