Allowance for Credit Losses (Allowance for Credit Losses Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Nonaccrual loans with no related allowance for credit losses	$ 83,400		$ 83,400
Loans reasonably expected to be modified into TDRs			4,400
Allowance for loan losses	373,109	$ 161,901	$ 373,109	$ 161,901	$ 253,412		$ 158,461	$ 159,622	$ 154,164
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201708Member
Provision for credit losses	135,053	24,580	$ 188,014	$ 35,204
Loan net charge-offs	15,400		20,700
Allowance for held-to-maturity securities losses	65	0	65	0			0
Held-to-maturity securities, provision (reversal) for credit losses	(5)		(9)
Cumulative effect adjustment from the adoption of ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses							47,344
Allowance for held-to-maturity securities losses						$ 74
Loans acquired with deteriorated credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses		531		531
Loans acquired with deteriorated credit quality | Cumulative effect adjustment from the adoption of ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses						11,000
Loans acquired without deteriorated credit quality | Cumulative effect adjustment from the adoption of ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses						3,200
Unfunded lending-related commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses	59,599	1,480	59,599	1,480			1,633
Unfunded lending-related commitments | Cumulative effect adjustment from the adoption of ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses						33,200
Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses	$ 313,510	$ 160,421	$ 313,510	$ 160,421			$ 156,828
Loans | Cumulative effect adjustment from the adoption of ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses						$ 14,200