Borrowings and Other Short-Term Liabilities - Short/Long-term and Other Short-term Borrowings (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Short-term borrowings:
Amount	$ 2,615,000	$ 2,035,000
Weighted Average Rate	2.44%	2.47%
Long-term borrowings:
Amount	$ 426,069	$ 426,002
Weighted Average Rate	2.11%	2.11%
Total borrowings	$ 3,041,069	$ 2,461,002
Total short-term and long-term borrowings, Weighted Average Rate	2.39%	2.41%
FHLB advances: 2.29% - 2.60% fixed-rate notes \| Minimum
Long-term borrowings:
Stated interest rate	2.29%
FHLB advances: 2.29% - 2.60% fixed-rate notes \| Maximum
Long-term borrowings:
Stated interest rate	2.60%
AFX short-term borrowings
Short-term borrowings:
Amount	$ 35,000	$ 0
Weighted Average Rate	2.41%	0.00%
FHLB Advances \| FHLB advances: 1.00% - 2.72% fixed-rate notes due 2019 to 2025
Long-term borrowings:
Amount	$ 410,073	$ 410,102
Weighted Average Rate	2.00%	2.00%
Advances payable from Federal Home Loan Banks	$ 410,000	$ 410,000
Purchase accounting premiums	$ 73	102
FHLB Advances \| FHLB advances: 1.00% - 2.72% fixed-rate notes due 2019 to 2025 \| Minimum
Long-term borrowings:
Stated interest rate	1.00%
FHLB Advances \| FHLB advances: 1.00% - 2.72% fixed-rate notes due 2019 to 2025 \| Maximum
Long-term borrowings:
Stated interest rate	2.72%
Subordinated debt obligations \| Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035
Long-term borrowings:
Amount	$ 11,648	$ 11,572
Weighted Average Rate	4.71%	4.85%
Advances payable	$ 15,000	$ 15,000
Purchase accounting discounts	$ 3,400	3,400
Subordinated debt obligations \| Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 \| Minimum
Long-term borrowings:
Spread on variable rate	1.45%
Subordinated debt obligations \| Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 \| Maximum
Long-term borrowings:
Spread on variable rate	2.85%
Subordinated debt obligations \| Subordinated debt obligations: floating-rate based on three-month LIBOR plus 3.25% due in 2032
Long-term borrowings:
Amount	$ 4,348	$ 4,328
Weighted Average Rate	5.84%	5.65%
Spread on variable rate	3.25%
Advances payable	$ 5,000	$ 5,000
Purchase accounting discounts	652	672
Collateralized customer deposits
Short-term borrowings:
Amount	$ 291,671	$ 382,687
Weighted Average Rate	0.70%	0.75%
FHLB Advances \| FHLB advances: 2.29% - 2.60% fixed-rate notes
Short-term borrowings:
Amount	$ 2,580,000	$ 2,035,000
Weighted Average Rate	2.44%	2.47%

Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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