Fair Value Measurements (Assets for which Nonrecurring Changes in Fair Value have been Recorded) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	$ 8,836,721		$ 8,836,721		$ 7,810,900
Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	8,670,844		8,670,844		$ 7,680,003
OREO and Repossessed Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	4,401	$ 1,557	4,401	$ 1,557
Losses from Nonrecurring Fair Value Changes	(243)	(203)	(360)	(221)
OREO and Repossessed Assets [Member] | Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	4,401	1,557	4,401	1,557
OREO and Repossessed Assets [Member] | Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0	0	0
Impaired Loans [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	101,353	15,385	101,353	15,385
Losses from Nonrecurring Fair Value Changes	(23,545)	(529)	(42,221)	(279)
Impaired Loans [Member] | Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	101,353	15,385	101,353	15,385
Impaired Loans [Member] | Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	$ 0	0	$ 0
Property Subject to Operating Lease [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	839		839
Losses from Nonrecurring Fair Value Changes			(691)
Property Subject to Operating Lease [Member] | Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	$ 839		$ 839