Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax assets
Allowance for loan losses	$ 63,952	$ 66,034
Net operating loss carryforwards	33,008	41,059
Net unrealized losses on investment securities available for sale	24,419	13,253
Employee benefits and deferred compensation	20,363	18,333
Tax credit carryforwards	20,088	19,175
Deferred revenue	10,189	12,311
Lease rental	2,526	2,549
Non-performing loan interest	2,442	10,388
Other	9,415	6,343
Total gross deferred tax assets	186,402	189,445
Less valuation allowance	0	(3,431)
Total deferred tax assets	186,402	186,014
Deferred tax liabilities
Excess tax over financial statement depreciation	(31,260)	(8,080)
Other properties held for sale	(5,469)	(5,447)
Other	(8,539)	(6,699)
Total gross deferred income tax liabilities	(45,268)	(20,226)
Net deferred tax assets	$ 141,134	$ 165,788