Federal Home Loan Bank Advances and Long-Term Debt (FHLB Advances) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
FHLB advances	$ 323,891	$ 321,643
FHLB advances that will mature in the next five years
Available borrowing capacity from FHLB advances	$ 6,830,000	$ 5,650,000
FHLB Advances
Debt Instrument [Line Items]
Weighted-average rate (as a percent)	1.85%	1.13%
FHLB advances that will mature in the next five years
2018	$ 0
2019	81,300
2020	0
2021	0
2022	242,600
Thereafter	$ 0
FHLB Advances \| Minimum
Debt Instrument [Line Items]
Variable interest rate	0.67%	0.41%
FHLB Advances \| Maximum
Debt Instrument [Line Items]
Variable interest rate	1.95%	1.27%

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
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Amount of advances or credit lines available from the Federal Home Loan Bank (FHLB).

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