Loans Receivable and the Allowance for Credit Losses - Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 29,079	$ 29,307
Charge-offs	(1,497)	(1,355)
Recoveries	299	106
Credit loss expense(1)	19,322	1,594
Ending balance	51,187	29,652
Loans Receivable
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Accrued interest receivable	12,200
Agricultural
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,748	3,637
Charge-offs	(84)	(134)
Recoveries	25	7
Credit loss expense(1)	14	181
Ending balance	1,146	3,691
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	8,394	7,478
Charge-offs	(471)	(354)
Recoveries	213	48
Credit loss expense(1)	8,445	422
Ending balance	19,309	7,594
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	13,804	15,635
Charge-offs	(720)	(650)
Recoveries	8	8
Credit loss expense(1)	8,746	(195)
Ending balance	23,138	14,798
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,685	2,349
Charge-offs		(49)
Recoveries	7	9
Credit loss expense(1)	1,683	963
Ending balance	6,425	3,272
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	448	208
Charge-offs	(222)	(168)
Recoveries	46	34
Credit loss expense(1)	434	223
Ending balance	$ 1,169	$ 297