FDIC Indemnification Asset and True-up Payment Obligation (FDIC Indemnification Asset Roll Forward) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
FDIC Indemnification Asset [Roll Forward]
Balance	$ 14,411,000	$ 22,599,000	$ 97,378,000
Shared-loss agreements reimbursements expected from the FDIC	0	(1,573,000)	(55,723,000)
Increase (decrease) in expected credit losses to be covered under shared-loss agreements, net	0	3,391,000	2,503,000
FDIC indemnification asset, expense	(1,403,000)	(8,040,000)	36,398,000
Final settlement with the FDIC on commercial loans	0	0	(1,589,000)
Net (reimbursements) expenses incurred under shared-loss agreements	0	(1,966,000)	16,428,000
Shared-loss termination benefit	(15,814,000)	0	0
Balance	0	14,411,000	22,599,000
True-up payment obligation [Roll Forward]
Balance	26,786,000	24,658,000	21,981,000
Change in true-up payment obligation expense	0	2,128,000	2,677,000
Shared-loss termination settlement, liability	(26,786,000)	0	0
Balance	$ 0	$ 26,786,000	$ 24,658,000