Business Segment Reporting - Core Earnings - Business Segments (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments									4
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	$ 42,216	$ 45,058	$ 43,933	$ 43,229	$ 41,283	$ 39,562	$ 39,731	$ 37,071	$ 174,436	$ 157,647	$ 140,274
Less: reconciling adjustments(1)(2)(3)									0	0	0
Net Effective Spread									0	0	0
Guarantee and commitment fees	3,506	3,490	3,481	3,499	3,484	3,314	3,472	3,844	13,976	14,114	14,868
Other Non-Interest Income (Expense), Excluding Guarantee and Commitment Fees									(2,236)	3,398	5,600
Noninterest Income	(682)	(4,439)	(6,380)	(239)	(2,673)	(4,299)	(3,744)	(6,796)	(11,740)	(17,512)	(20,468)
Provision for Loan Losses Expensed	146	99	424	(431)	474	270	327	637	238	1,708	1,065
Provision for/(release of) reserve for losses									97	50	(63)
Noninterest Expense, Excluding Loan, Lease and Other Losses									49,819	42,715	40,383
Noninterest Expense	(13,703)	(11,650)	(12,921)	(11,642)	(10,210)	(10,616)	(11,390)	(10,549)	(49,916)	(42,765)	(40,320)
Net income	29,049	37,748	36,968	32,257	33,272	32,975	31,758	32,681	136,022	130,686	119,357
ERROR in label resolution.	(22,856)	(29,769)	(29,636)	(25,819)	(20,006)	(21,782)	(20,634)	(21,895)	(108,080)	(84,317)	(77,300)
Preferred Stock Dividends, Income Statement Impact	(3,296)	(3,295)	(3,296)	(3,295)	(3,296)	(3,295)	(3,296)	(3,295)	(13,182)	(13,182)	(13,182)
Less: Net loss attributable to non-controlling interest					0	0	150	15	0	165	34
Net Income (Loss) Available to Common Stockholders, Basic	19,560	26,474	26,340	22,524	16,710	18,487	17,488	18,615	94,898	71,300	64,152
Total Assets	18,694,328				17,792,274				18,694,328	17,792,274	15,606,020
Segment Reporting Information, Additional Information [Abstract]
On and Off Balance Sheet Program Assets, At Principal Balance	19,724,524				19,007,311				19,724,524	19,007,311	17,399,475
Income tax expense	6,193	$ 7,979	$ 7,332	$ 6,438	13,266	$ 11,193	$ 11,124	$ 10,786	27,942	46,369	42,057
Farm & Ranch [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income									62,951	54,290	47,219
Less: reconciling adjustments(1)(2)(3)									(9,889)	(8,922)	(7,729)
Net Effective Spread									53,062	45,368	39,490
Guarantee and commitment fees									17,976	17,175	15,542
Other Non-Interest Income (Expense), Excluding Guarantee and Commitment Fees									1,371	2,449	539
Noninterest Income									(19,347)	(19,624)	(16,081)
Provision for Loan Losses Expensed									238	1,708	1,065
Provision for/(release of) reserve for losses									97	50	(63)
Noninterest Expense, Excluding Loan, Lease and Other Losses									19,026	16,554	16,206
Noninterest Expense									(19,123)	(16,604)	(16,143)
Segment core earnings before income taxes									53,048	46,680	38,363
Preferred Stock Dividends, Income Statement Impact									0	0	0
Less: Net loss attributable to non-controlling interest										0	0
Segment core earnings									41,908	30,342	24,935
Total Assets	4,701,736				4,274,693				4,701,736	4,274,693	3,582,098
Segment Reporting Information, Additional Information [Abstract]
On and Off Balance Sheet Program Assets, At Principal Balance	7,233,972				6,867,586				7,233,972	6,867,586	6,139,304
Income tax expense									11,140	16,338	13,428
Segment core earnings before preferred stock dividends and attibution of income to non-controlling interest - preferred stock dividends									41,908	30,342	24,935
USDA Guarantees [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income									20,554	21,106	21,865
Less: reconciling adjustments(1)(2)(3)									(2,499)	(2,287)	(3,210)
Net Effective Spread									18,055	18,819	18,655
Guarantee and commitment fees									797	456	101
Other Non-Interest Income (Expense), Excluding Guarantee and Commitment Fees									20	43	222
Noninterest Income									(817)	(499)	(323)
Provision for Loan Losses Expensed									0	0	0
Provision for/(release of) reserve for losses									0	0	0
Noninterest Expense, Excluding Loan, Lease and Other Losses									5,309	4,384	4,200
Noninterest Expense									(5,309)	(4,384)	(4,200)
Segment core earnings before income taxes									13,563	14,934	14,778
Preferred Stock Dividends, Income Statement Impact									0	0	0
Less: Net loss attributable to non-controlling interest										0	0
Segment core earnings									10,715	9,707	9,605
Total Assets	2,240,906				2,195,189				2,240,906	2,195,189	2,096,503
Segment Reporting Information, Additional Information [Abstract]
On and Off Balance Sheet Program Assets, At Principal Balance	2,515,620				2,352,214				2,515,620	2,352,214	2,094,375
Income tax expense									2,848	5,227	5,173
Segment core earnings before preferred stock dividends and attibution of income to non-controlling interest - preferred stock dividends									10,715	9,707	9,605
Rural Utilities [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income									12,505	11,598	11,739
Less: reconciling adjustments(1)(2)(3)									(922)	(539)	(1,771)
Net Effective Spread									11,583	11,059	9,968
Guarantee and commitment fees									1,599	1,914	1,694
Other Non-Interest Income (Expense), Excluding Guarantee and Commitment Fees									33	20	2
Noninterest Income									(1,632)	(1,934)	(1,696)
Provision for Loan Losses Expensed									0	0	0
Provision for/(release of) reserve for losses									0	0	0
Noninterest Expense, Excluding Loan, Lease and Other Losses									3,062	2,430	2,856
Noninterest Expense									(3,062)	(2,430)	(2,856)
Segment core earnings before income taxes									10,153	10,563	8,808
Preferred Stock Dividends, Income Statement Impact									0	0	0
Less: Net loss attributable to non-controlling interest										0	0
Segment core earnings									8,020	6,867	5,725
Total Assets	945,282				1,088,986				945,282	1,088,986	1,012,014
Segment Reporting Information, Additional Information [Abstract]
On and Off Balance Sheet Program Assets, At Principal Balance	1,592,115				1,882,633				1,592,115	1,882,633	1,878,110
Income tax expense									2,133	3,696	3,083
Segment core earnings before preferred stock dividends and attibution of income to non-controlling interest - preferred stock dividends									8,020	6,867	5,725
Institutional Credit [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income									69,321	59,842	48,756
Less: reconciling adjustments(1)(2)(3)									(7,884)	(3,505)	(3,184)
Net Effective Spread									61,437	56,337	45,572
Guarantee and commitment fees									360	805	1,833
Other Non-Interest Income (Expense), Excluding Guarantee and Commitment Fees									0	0	0
Noninterest Income									(360)	(805)	(1,833)
Provision for Loan Losses Expensed									0	0	0
Provision for/(release of) reserve for losses									0	0	0
Noninterest Expense, Excluding Loan, Lease and Other Losses									8,011	6,439	3,786
Noninterest Expense									(8,011)	(6,439)	(3,786)
Segment core earnings before income taxes									53,786	50,703	43,619
Preferred Stock Dividends, Income Statement Impact									0	0	0
Less: Net loss attributable to non-controlling interest										0	0
Segment core earnings									42,491	32,957	28,354
Total Assets	8,089,410				7,627,749				8,089,410	7,627,749	6,008,574
Segment Reporting Information, Additional Information [Abstract]
On and Off Balance Sheet Program Assets, At Principal Balance	8,382,817				7,904,878				8,382,817	7,904,878	7,287,686
Income tax expense									11,295	17,746	15,265
Segment core earnings before preferred stock dividends and attibution of income to non-controlling interest - preferred stock dividends									42,491	32,957	28,354
Corporate Segment [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income									9,105	10,811	10,695
Less: reconciling adjustments(1)(2)(3)									(2,047)	(1,091)	(1,308)
Net Effective Spread									7,058	9,720	9,387
Guarantee and commitment fees									0	0	0
Other Non-Interest Income (Expense), Excluding Guarantee and Commitment Fees									(913)	171	1,322
Noninterest Income									913	(171)	(1,322)
Provision for Loan Losses Expensed									0	0	0
Provision for/(release of) reserve for losses									0	0	0
Noninterest Expense, Excluding Loan, Lease and Other Losses									14,411	12,908	13,335
Noninterest Expense									(14,411)	(12,908)	(13,335)
Segment core earnings before income taxes									(8,266)	(3,017)	(2,626)
Preferred Stock Dividends, Income Statement Impact									(13,182)	(13,182)	(13,182)
Less: Net loss attributable to non-controlling interest										165	34
Segment core earnings									(19,087)	(14,242)	(15,138)
Total Assets	2,716,994				2,605,657				2,716,994	2,605,657	2,906,831
Segment Reporting Information, Additional Information [Abstract]
Income tax expense									(2,361)	(1,792)	(636)
Segment core earnings before preferred stock dividends and attibution of income to non-controlling interest - preferred stock dividends									(5,905)	(1,225)	(1,990)
Segment Reconciling Items [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income									0	0	0
Less: reconciling adjustments(1)(2)(3)									23,241	16,344	17,202
Net Effective Spread									23,241	16,344	17,202
Guarantee and commitment fees									(6,756)	(6,236)	(4,302)
Other Non-Interest Income (Expense), Excluding Guarantee and Commitment Fees									(2,747)	715	3,515
Noninterest Income									9,503	5,521	787
Provision for Loan Losses Expensed									0	0	0
Provision for/(release of) reserve for losses									0	0	0
Noninterest Expense, Excluding Loan, Lease and Other Losses									0	0	0
Noninterest Expense									0	0	0
Segment core earnings before income taxes									13,738	10,823	16,415
Preferred Stock Dividends, Income Statement Impact									0	0	0
Less: Net loss attributable to non-controlling interest										0	0
Segment core earnings									10,851	5,669	10,671
Total Assets	0				0				0	0	0
Segment Reporting Information, Additional Information [Abstract]
On and Off Balance Sheet Program Assets, At Principal Balance	$ 0				$ 0				0	0	0
Income tax expense									2,887	5,154	5,744
Segment core earnings before preferred stock dividends and attibution of income to non-controlling interest - preferred stock dividends									$ 10,851	$ 5,669	$ 10,671