Loans (Details) - Loan Portfolio (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Loans and Leases Receivable Disclosure [Abstract]
Commercial and industrial	$ 2,073,018		$ 1,830,638
Agricultural	330,626		321,702
Commercial real estate:
Office, retail, and industrial	1,312,401		1,353,685
Multi-family	350,430		332,873
Construction	195,109		186,197
Other commercial real estate	798,324		807,071
Total commercial real estate	2,656,264		2,679,826
Total corporate loans	5,059,908		4,832,166
Home equity	485,085		427,020
1-4 family mortgages	241,156		275,992
Installment	57,308		44,827
Total consumer loans	783,549		747,839
Total loans, excluding covered loans	5,843,457		5,580,005
Covered loans	104,867	[1]	134,355	[1]
Total Loans	5,948,324		5,714,360
Deferred loan fees included in total loans	4,051		4,656
Overdrawn demand deposits included in total loans	$ 3,980		$ 5,047

[1] For information on covered loans, refer to Note 5, “Acquired Loans.”