Borrowings and Other Short-Term Liabilities - Short/Long-term and Other Short-term Borrowings (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Short-term borrowings:
Amount	$ 2,095,000	$ 2,000,000
Weighted Average Rate	2.04%	1.39%
Long-term borrowings:
Amount	$ 330,956	$ 372,882
Weighted Average Rate	1.45%	1.47%
Total borrowings	$ 2,425,956	$ 2,372,882
Total short-term and long-term borrowings, Weighted Average Rate	1.96%	1.40%
FHLB advances: 1.96% - 2.09% fixed-rate notes \| Minimum
Long-term borrowings:
Stated interest rate	1.96%
FHLB advances: 1.96% - 2.09% fixed-rate notes \| Maximum
Long-term borrowings:
Stated interest rate	2.09%
FHLB Advances \| FHLB advances: 0.92% - 7.44% fixed-rate notes due 2017 to 2020
Long-term borrowings:
Amount	$ 315,149	$ 337,204
Weighted Average Rate	1.28%	1.26%
Advances payable from Federal Home Loan Banks	$ 315,000	$ 337,000
Purchase accounting premiums	$ 100	200
FHLB Advances \| FHLB advances: 0.92% - 7.44% fixed-rate notes due 2017 to 2020 \| Minimum
Long-term borrowings:
Stated interest rate	1.00%
FHLB Advances \| FHLB advances: 0.92% - 7.44% fixed-rate notes due 2017 to 2020 \| Maximum
Long-term borrowings:
Stated interest rate	2.60%
Line of Credit
Long-term borrowings:
Amount	$ 0	$ 19,963
Weighted Average Rate	0.00%	3.10%
Spread on variable rate	1.75%
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	$ 11,498	$ 11,425
Weighted Average Rate	4.56%	3.69%
Advances payable	$ 15,000	$ 15,000
Purchase accounting discounts	$ 3,500	3,600
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	$ 4,309	$ 4,290
Weighted Average Rate	5.56%	4.59%
Spread on variable rate	3.25%
Advances payable	$ 5,000	$ 5,000
Purchase accounting discounts	700	700
Collateralized customer deposits
Short-term borrowings:
Amount	$ 378,938	$ 415,236
Weighted Average Rate	0.61%	0.44%
FHLB Advances \| FHLB advances: 1.96% - 2.09% fixed-rate notes
Short-term borrowings:
Amount	$ 2,075,000	$ 2,000,000
Weighted Average Rate	2.02%	1.39%
FHLB Advances \| Line of Credit
Short-term borrowings:
Amount	$ 20,000	$ 0
Weighted Average Rate	3.73%	0.00%

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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