Allowance for Credit Losses (Impaired Loans) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Interest Recognized
Total trouble debt restructuring	$ 6,010,000		$ 7,788,000
Amount of loans with some degree of payment deferred	$ 1,270,763,000
Term of receivable (in years)	2 years
Loans	$ 7,024,380,000		6,894,946,000
Amount of loans approved and closed	$ 461,133,000
Period of charge off for past due unsecured commercial loans	90 days
Class of Financing Receivable
Recorded investment:
Total impaired loans with related allowance		$ 25,922,000	636,000
Total impaired loans with no related allowance			12,039,000
Unpaid principal balance:
Total impaired loans with an allowance recorded			685,000
Total impaired loans with no related allowance recorded			13,255,000
Related Allowance			365,000
Average recorded investment:
Total impaired loans with an allowance recorded			645,000
Total impaired loans with no related allowance recorded		30,619,000	52,945,000
Interest Recognized
Total impaired loans with an allowance recorded		26,851,000
Total impaired loans with no related allowance recorded		90,000	365,000
Commercial
Interest Recognized
Total trouble debt restructuring			32,000
Loans	$ 1,369,011,000		1,292,660,000
Commercial | Class of Financing Receivable
Recorded investment:
Total impaired loans with related allowance		1,325,000	510,000
Total impaired loans with no related allowance			1,425,000
Unpaid principal balance:
Total impaired loans with an allowance recorded			516,000
Total impaired loans with no related allowance recorded			1,516,000
Related Allowance			249,000
Average recorded investment:
Total impaired loans with an allowance recorded			514,000
Total impaired loans with no related allowance recorded		17,370,000	18,794,000
Interest Recognized
Total impaired loans with an allowance recorded		1,908,000
Total impaired loans with no related allowance recorded		1,000	2,000
Real estate - construction
Interest Recognized
Loans	2,216,740,000		2,185,883,000
Real estate - construction | Class of Financing Receivable
Recorded investment:
Total impaired loans with related allowance		134,000	126,000
Total impaired loans with no related allowance			812,000
Unpaid principal balance:
Total impaired loans with an allowance recorded			169,000
Total impaired loans with no related allowance recorded			1,133,000
Related Allowance			116,000
Average recorded investment:
Total impaired loans with an allowance recorded			131,000
Total impaired loans with no related allowance recorded		1,924,000	1,737,000
Interest Recognized
Total impaired loans with an allowance recorded		169,000
Commercial Real Estate: Farmland and Commercial
Interest Recognized
Loans	1,933,365,000		1,896,747,000
Commercial Real Estate: Farmland and Commercial | Class of Financing Receivable
Recorded investment:
Total impaired loans with related allowance		24,463,000
Total impaired loans with no related allowance			1,208,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded			1,841,000
Average recorded investment:
Total impaired loans with no related allowance recorded		2,305,000	22,357,000
Interest Recognized
Total impaired loans with an allowance recorded		24,774,000
Commercial Real Estate: Multifamily
Interest Recognized
Loans	202,450,000		190,430,000
Commercial Real Estate: Multifamily | Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance			165,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded			168,000
Average recorded investment:
Total impaired loans with no related allowance recorded		506,000	651,000
Residential First Lien
Interest Recognized
Total trouble debt restructuring	3,857,000		5,608,000
Loans	431,588,000		433,901,000
Residential First Lien | Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance			6,278,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded			6,445,000
Average recorded investment:
Total impaired loans with no related allowance recorded		6,239,000	6,988,000
Interest Recognized
Total impaired loans with no related allowance recorded		75,000	309,000
Residential Junior Lien
Interest Recognized
Total trouble debt restructuring	680,000		692,000
Loans	686,604,000		706,476,000
Residential Junior Lien | Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance			692,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded			692,000
Average recorded investment:
Total impaired loans with no related allowance recorded		912,000	1,023,000
Interest Recognized
Total impaired loans with no related allowance recorded		11,000	42,000
Consumer
Interest Recognized
Total trouble debt restructuring	1,217,000		1,192,000
Loans	45,440,000		47,800,000
Consumer | Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance			1,195,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded			1,196,000
Average recorded investment:
Total impaired loans with no related allowance recorded		1,075,000	1,117,000
Foreign
Interest Recognized
Total trouble debt restructuring	256,000		264,000
Loans	$ 139,182,000		141,049,000
Foreign | Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance			264,000
Unpaid principal balance:
Total impaired loans with no related allowance recorded			264,000
Average recorded investment:
Total impaired loans with no related allowance recorded		288,000	278,000
Interest Recognized
Total impaired loans with no related allowance recorded		$ 3,000	$ 12,000
Paycheck Protection Program Loans
Interest Recognized
Interest rate on receivable	1.00%
Number of loans approved and closed	4,528