FDIC loss-share asset and true-up payment obligation - Activity in the FDIC loss share indemnification asset (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018
FDIC Indemnification Asset [Roll Forward]
Beginning Balance	$ 46,316
FDIC loss-sharing termination agreement	(45,659)
Amortization	(934)
Credit impairment losses to be covered under loss sharing agreements	104
Reimbursable expenses	537
Net payment from FDIC under loss-sharing agreements	(364)
Ending Balance	0
Balance due to the FDIC for recoveries on covered assets	0
FDIC loss-share asset net	$ 0	$ 44,500