Fair Values of Financial Instruments, Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial assets [Abstract]
HTM securities	$ 481,871	$ 525,050
Financial liabilities [Abstract]
Time deposits	806,766	872,411
Long-term debt	88,869	104,087
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] | Level 2 [Member]
Financial assets [Abstract]
HTM securities	484,073	527,948
Financial liabilities [Abstract]
Time deposits	806,766	872,411
Long-term debt	88,869	104,087
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] | Level 3 [Member]
Financial assets [Abstract]
Net Loans	6,515,273	6,132,857
Estimated Fair Value [Member] | Level 2 [Member]
Financial assets [Abstract]
HTM securities	481,871	525,050
Financial liabilities [Abstract]
Time deposits	801,294	868,153
Long-term debt	88,346	104,113
Junior subordinated debt	104,593	102,262
Estimated Fair Value [Member] | Level 3 [Member]
Financial assets [Abstract]
Net Loans	$ 6,651,931	$ 6,273,233