Fair Value Measurements (Narrative) (Details)		3 Months Ended		6 Months Ended	12 Months Ended
		Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) loan	Dec. 31, 2019 USD ($)	Dec. 31, 2014 USD ($) loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount		$ 0	$ 0	$ 0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount		0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net		0	$ 0
Cash and cash equivalents		480,700,000		480,700,000	$ 944,500,000
Collateral dependent loans		10,500,000		10,500,000
Specific reserves and other write downs on impaired loans		$ 2,700,000		$ 2,700,000
Number of troubled debt restructured loans | loan		11		11
Troubled debt restructured loans balance				$ 1,696,000	2,084,000
Troubled debt restructured loans, specific reserve		$ 510,000		510,000
Other real estate owned		0		0	0
Walnut Street [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, face value						$ 267,600,000
Proceeds from Sale of Loans Receivable						209,600,000
Notes Payable						$ 193,600,000
Number of notes | loan						2
Walnut Street [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes						$ 178,200,000
Debt Instrument, Interest Rate, Stated Percentage						1.50%
Walnut Street [Member] | Junior Subordinated Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Junior Subordinated Notes						$ 15,400,000
Debt Instrument, Interest Rate, Stated Percentage						10.00%
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateral dependent loans	[1]	$ 7,828,000		$ 7,828,000	$ 3,651,000

[1] The method of valuation approach for the collateral dependent loans was the market value approach based upon appraisals of the underlying collateral by external appraisers, reduced by 7% to 10% for estimated selling costs. Intangible assets are valued based upon internal analyses.