Fair Value Measurements and Fair Value of Financial Instruments, Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial assets [Abstract]
HTM securities	$ 754,995	$ 778,675
Carrying Amount [Member] | Level 2 [Member]
Financial assets [Abstract]
HTM securities	744,601	783,599
Financial liabilities [Abstract]
Time deposits	976,567	930,678
Long-term debt	84,267	73,724
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] | Level 3 [Member]
Financial assets [Abstract]
Net loans	6,906,770	6,822,147
Estimated Fair Value [Member] | Level 2 [Member]
Financial assets [Abstract]
HTM securities	754,995	778,675
Financial liabilities [Abstract]
Time deposits	973,822	920,534
Long-term debt	84,878	73,927
Junior subordinated debt	104,914	100,114
Estimated Fair Value [Member] | Level 3 [Member]
Financial assets [Abstract]
Net loans	$ 7,199,147	$ 6,754,460