Borrowings (Schedule of Short- and Long-term Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2016
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 372,882	$ 597,847
Long-term borrowings, Weighted Average Rate	1.47%	1.63%
Total short-term and long-term borrowings	$ 2,788,118	$ 1,765,894
Total short-term and long-term borrowings, Weighted Average Rate	1.26%	0.89%
FHLB advances: 1.25% - 1.50% fixed-rate notes | Minimum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	1.25%
FHLB advances: 1.25% - 1.50% fixed-rate notes | Maximum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	1.50%
Federal Home Loan Bank Advances | FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 337,204	$ 438,538
Long-term borrowings, Weighted Average Rate	1.26%	1.24%
Advances payable from Federal Home Loan Banks	$ 337,000	$ 437,800
Purchase accounting premiums	$ 200	700
Federal Home Loan Bank Advances | FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020 | Minimum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	0.92%
Federal Home Loan Bank Advances | FHLB advances: 0.92% - 2.60% fixed-rate notes due 2018 to 2020 | Maximum
Short Term Borrowings and Long Term Debt [Line Items]
Stated interest rate	2.60%
Securities sold under agreements to repurchase | Securities sold under agreements to repurchase
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 0	$ 19,144
Long-term borrowings, Weighted Average Rate	0.00%	3.17%
Advances payable from Federal Home Loan Banks		$ 19,000
Purchase accounting premiums		100
Line of Credit
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 19,963	$ 124,625	$ 125,000
Long-term borrowings, Weighted Average Rate	3.10%	2.52%
Line of Credit | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis 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
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 11,425	$ 11,285
Long-term borrowings, Weighted Average Rate	3.69%	3.14%
Purchase accounting discounts	$ 3,600	$ 3,700
Advances payable	$ 15,000	15,000
Subordinated Debt Obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 | Minimum | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis 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 | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis 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
Short Term Borrowings and Long Term Debt [Line Items]
Long-term borrowings, Amount	$ 4,290	$ 4,255
Long-term borrowings, Weighted Average Rate	4.59%	4.25%
Purchase accounting discounts	$ 700	$ 700
Advances payable	$ 5,000	5,000
Subordinated Debt Obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 3.25% due in 2032 | LIBOR
Short Term Borrowings and Long Term Debt [Line Items]
Basis spread on variable rate	3.25%
Securities sold under agreements to repurchase
Short Term Borrowings and Long Term Debt [Line Items]
Short-term borrowings, Amount	$ 415,236	$ 343,047
Weighted average interest rate	0.44%	0.16%
Federal Home Loan Bank Advances | FHLB advances: 1.25% - 1.50% fixed-rate notes
Short Term Borrowings and Long Term Debt [Line Items]
Short-term borrowings, Amount	$ 2,000,000	$ 825,000
Weighted average interest rate	1.39%	0.65%