Fair Value Measurements (Carrying Amounts and Estimated Fair Values) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment securities:
Held-to-maturity	$ 662,906	$ 608,531
Bank-owned life insurance	147,600	143,700
Deposits without defined maturities
Short-term borrowings	2,000,000	825,000
Long-term borrowings	372,882	597,847
Nonrecurring
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis	73,518	63,572
Nonrecurring | Impaired loans
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis		62,184
Level 3 | Nonrecurring
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis	73,518	63,572
Level 3 | Nonrecurring | Impaired loans
Deposits without defined maturities
Assets measured at fair value on a nonrecurring basis	70,619	62,184
Carrying Amount | Level 1
Financial assets:
Cash and cash equivalents	455,991	474,402
Carrying Amount | Level 2
Investment securities:
Held-to-maturity	676,593	622,927
Nonmarketable equity securities	180,091	97,350
Interest receivable	50,710	42,235
Bank-owned life insurance	147,584	143,718
Deposits without defined maturities
Deposits without defined maturities	10,425,596	9,862,755
Time deposits	3,217,207	3,010,367
Total deposits	13,642,803	12,873,122
Interest payable	6,329	5,415
Securities sold under agreements to repurchase with customers	415,236	343,047
Short-term borrowings	2,000,000	825,000
Long-term borrowings	372,882	597,847
Carrying Amount | Level 3
Investment securities:
Held-to-maturity	500	500
Net loans	14,063,380	12,912,511
Fair Value | Level 1
Financial assets:
Cash and cash equivalents	455,991	474,402
Fair Value | Level 2
Investment securities:
Held-to-maturity	662,516	608,221
Nonmarketable equity securities	180,091	97,350
Interest receivable	50,710	42,235
Bank-owned life insurance	147,584	143,718
Deposits without defined maturities
Deposits without defined maturities	10,425,596	9,862,755
Time deposits	3,225,847	3,010,048
Total deposits	13,651,443	12,872,803
Interest payable	6,329	5,415
Securities sold under agreements to repurchase with customers	415,236	343,047
Short-term borrowings	1,999,137	825,000
Long-term borrowings	367,984	591,227
Fair Value | Level 3
Investment securities:
Held-to-maturity	390	310
Net loans	$ 14,114,545	$ 13,069,315