Fair Value Measurements - Carrying Amounts and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investment securities:
Held-to-maturity	$ 640,043	$ 608,531
Nonrecurring
Deposits:
Assets, Fair Value Disclosure, Nonrecurring	67,505	63,572
Nonrecurring | Impaired originated loans
Deposits:
Assets, Fair Value Disclosure, Nonrecurring	63,694	62,184
Level 3 | Nonrecurring
Deposits:
Assets, Fair Value Disclosure, Nonrecurring	67,505	63,572
Level 3 | Nonrecurring | Impaired originated loans
Deposits:
Assets, Fair Value Disclosure, Nonrecurring	63,694	62,184
Carrying Amount | Level 1
Financial assets:
Cash and cash equivalents	619,241	474,402
Carrying Amount | Level 2
Investment securities:
Held-to-maturity	645,105	622,927
Nonmarketable equity securities	180,196	97,350
Interest receivable	45,832	42,235
Bank-owned life insurance	145,671	143,718
Deposits:
Deposits without defined maturities	10,217,235	9,862,755
Time deposits	2,987,132	3,010,367
Total deposits	13,204,367	12,873,122
Interest payable	5,112	5,415
Securities sold under agreements to repurchase with customers	310,042	343,047
Short-term borrowings	2,050,000	825,000
Long-term borrowings	435,852	597,847
Carrying Amount | Level 3
Investment securities:
Held-to-maturity	500	500
Net loans	13,583,575	12,912,511
Fair Value | Level 1
Financial assets:
Cash and cash equivalents	619,241	474,402
Fair Value | Level 2
Investment securities:
Held-to-maturity	639,683	608,221
Nonmarketable equity securities	180,196	97,350
Interest receivable	45,832	42,235
Bank-owned life insurance	145,671	143,718
Deposits:
Deposits without defined maturities	10,217,235	9,862,755
Time deposits	2,987,779	3,010,048
Total deposits	13,205,014	12,872,803
Interest payable	5,112	5,415
Securities sold under agreements to repurchase with customers	310,042	343,047
Short-term borrowings	2,048,744	825,000
Long-term borrowings	431,345	591,227
Fair Value | Level 3
Investment securities:
Held-to-maturity	360	310
Net loans	$ 13,758,368	$ 13,069,315