Fair Value Measurements and Fair Value of Financial Instruments, Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financial assets [Abstract]
HTM securities	$ 642,325	$ 641,262
Carrying Amount [Member] | Level 2 [Member]
Financial assets [Abstract]
HTM securities	621,359	630,074
Financial liabilities [Abstract]
Time deposits	843,279	861,193
Long-term debt	64,183	64,211
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] | Level 3 [Member]
Financial assets [Abstract]
Net loans	7,153,858	7,074,864
Estimated Fair Value [Member] | Level 2 [Member]
Financial assets [Abstract]
HTM securities	642,325	641,262
Financial liabilities [Abstract]
Time deposits	847,284	858,085
Long-term debt	64,815	64,373
Junior subordinated debt	89,368	105,694
Estimated Fair Value [Member] | Level 3 [Member]
Financial assets [Abstract]
Net loans	$ 7,210,148	$ 6,999,690