Acquisitions (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended
	Sep. 25, 2017	Oct. 01, 2016	Nov. 30, 2017	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Brokered deposits				$ 2,006,578	$ 1,961,125
Common stock, shares issued (in shares)				143,017,301	142,677,449
Common stock				$ 143,017	$ 142,678
Minimum
Business Acquisition [Line Items]
Period of additional annual payments				3 years
Maximum
Business Acquisition [Line Items]
Period of additional annual payments				5 years
World's Foremost Bank (WFB)
Business Acquisition [Line Items]
Brokered deposits	$ 1,100,000
Deposits portfolio, weighted average maturity, period	2 years 6 months 11 days
Weighted average rate of deposit, brokered	1.83%
Proceeds from fees	$ 75,000
Global One
Business Acquisition [Line Items]
Consideration transferred		$ 30,000
Common stock, shares issued (in shares)		821,000
Common stock		$ 26,600
Cash paid		$ 3,400
Earnout payment of stock and cash			$ 6,400
Earnout liability				$ 11,300
Global One | Minimum
Business Acquisition [Line Items]
Potential additional payments based on earnings, period		3 years
Global One | Maximum
Business Acquisition [Line Items]
Potential additional payments based on earnings, period		5 years