Fair Value of Assets & Liabilities - Summary Of Changes In Level 3 Assets And Liabilities Measured At Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ (9,425)	$ (5,700)	$ (5,645)	$ (6,245)
Net income	(529)	(129)	(4,904)	(179)
Purchases	(28,100)	0	(28,100)	0
Sales	0		0	0
Settlements	3,842	299	4,437	894
Net transfers into/(out of) Level 3	0	0	0	0
Ending balance	(34,212)	(5,530)	(34,212)	(5,530)
Net unrealized gains/(losses) included in net income	(530)	(129)	(4,904)	(179)
Trading securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,724	2,464	2,151	2,573
Net income	33	92	173	380
Purchases	0	0	0	0
Sales	0		0	0
Settlements	(165)	(251)	(732)	(648)
Net transfers into/(out of) Level 3	0	0	0	0
Ending balance	1,592	2,305	1,592	2,305
Net unrealized gains/(losses) included in net income	(3)	62	59	264
Interest- only strips- AFS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5,787	1,163	1,270	0
Net income	(456)	(160)	840	107
Purchases	0	0	0	1,413
Sales	(2,034)		(11,227)	(3,291)
Settlements	0	0	0	0
Net transfers into/(out of) Level 3	7,064	2,120	19,478	4,894
Ending balance	10,361	3,123	10,361	3,123
Net unrealized gains/(losses) included in net income	(215)	(72)	(279)	(122)
Loans held- for-sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	16,718	20,587	18,926	21,924
Net income	277	390	986	1,722
Purchases	0	43	62	118
Sales	0		0	0
Settlements	(759)	(939)	(3,382)	(3,340)
Net transfers into/(out of) Level 3	0	0	(356)	(343)
Ending balance	16,236	20,081	16,236	20,081
Net unrealized gains/(losses) included in net income	$ 277	$ 390	$ 986	$ 1,722

Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of unrealized gain (loss) recognized in the income statement for a financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sales of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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