Fair Value Measurements - Carrying Amounts and Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investment securities:
Held-to-maturity	$ 639,800	$ 608,531
Carrying Amount | Level 1
Financial assets:
Cash and cash equivalents	441,780	474,402
Carrying Amount | Level 2
Investment securities:
Held-to-maturity	646,692	622,927
Nonmarketable equity securities	129,939	97,350
Interest receivable	45,863	42,235
Deposits:
Deposits without defined maturities	10,213,518	9,862,755
Time deposits	2,918,829	3,010,367
Total deposits	13,132,347	12,873,122
Interest payable	5,225	5,415
Securities sold under agreements to repurchase with customers	398,910	343,047
Short-term borrowings	900,000	825,000
Long-term borrowings	490,876	597,847
Carrying Amount | Level 3
Investment securities:
Held-to-maturity	500	500
Net loans	13,194,618	12,912,511
Fair Value | Level 1
Financial assets:
Cash and cash equivalents	441,780	474,402
Fair Value | Level 2
Investment securities:
Held-to-maturity	639,450	608,221
Nonmarketable equity securities	129,939	97,350
Interest receivable	45,863	42,235
Deposits:
Deposits without defined maturities	10,213,518	9,862,755
Time deposits	2,919,153	3,010,048
Total deposits	13,132,671	12,872,803
Interest payable	5,225	5,415
Securities sold under agreements to repurchase with customers	398,910	343,047
Short-term borrowings	899,777	825,000
Long-term borrowings	486,161	591,227
Fair Value | Level 3
Investment securities:
Held-to-maturity	350	310
Net loans	$ 13,347,793	$ 13,069,315