FHLB Advances, Other Borrowings and Subordinated Notes (Narrative) (Details) $ in Millions	1 Months Ended								3 Months Ended	6 Months Ended		12 Months Ended	24 Months Ended	48 Months Ended	54 Months Ended	62 Months Ended	65 Months Ended	73 Months Ended	77 Months Ended
	May 31, 2020 CAD ($)	Jan. 31, 2020 CAD ($)	May 31, 2019 CAD ($)	Feb. 28, 2019 CAD ($)	Jun. 30, 2018 CAD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2015 CAD ($)	Dec. 31, 2014 CAD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) building Rate	Jun. 30, 2019 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 CAD ($)	Dec. 31, 2017 CAD ($)	Jun. 30, 2018 CAD ($)	Feb. 28, 2019 CAD ($)	May 31, 2019 CAD ($)	Jan. 31, 2020 CAD ($)	May 31, 2020 CAD ($)	Apr. 01, 2020 USD ($)	Mar. 31, 2020	Dec. 31, 2019 USD ($)	Sep. 18, 2018 USD ($)
Debt Instrument [Line Items]
Notes payable									$ 133,776,000	$ 112,401,000	$ 133,776,000											$ 123,090,000	$ 150,000,000.0
Short-term borrowings									10,182,000	8,458,000	10,182,000											20,520,000
Other borrowings									47,072,000	65,980,000	47,072,000											46,447,000
Secured borrowings									227,027,000	321,696,000	227,027,000											228,117,000
Subordinated notes									436,021,000	436,298,000	436,021,000											436,095,000
Proceeds from the issuance of subordinated notes, net										0	296,741,000
Term Facility
Debt Instrument [Line Items]
Notes payable										112,400,000													150,000,000.0
Revolving Credit Facility
Debt Instrument [Line Items]
Notes payable																							50,000,000.0
Amount outstanding										$ 0
Subordinated debt maturing June 2029
Debt Instrument [Line Items]
Proceeds from the issuance of subordinated notes, net									296,700,000
Base Rate Loan | Base Rate | Term Facility
Debt Instrument [Line Items]
Basis spread on variable rate										0.75%
Base Rate Loan | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate										0.50%
Base Rate Loan | Federal Funds Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate										0.50%
Base Rate Loan | Eurodollar rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate										1.00%
Eurodollar Rate Loan | London Interbank Offered Rate (LIBOR) | Term Facility
Debt Instrument [Line Items]
Basis spread on variable rate										1.25%
Eurodollar Rate Loan | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate										1.25%
Line of Credit
Debt Instrument [Line Items]
Loan agreement with unaffiliated banks																							$ 200,000,000.0
Revolving Credit Facility
Debt Instrument [Line Items]
Commitment fee | Rate										0.20%
Securities sold under repurchase agreements
Debt Instrument [Line Items]
Securities sold under agreements to repurchase									10,200,000		10,200,000											20,500,000
Securities sold under repurchase agreements | Overnight Sweep Collateral
Debt Instrument [Line Items]
Securities sold under agreements to repurchase										$ 8,458,000
Pledged financial instruments										$ 20,536,000
Fixed Rate Promissory Note
Debt Instrument [Line Items]
Number of properties securing debt | building										3
Other borrowings									47,100,000	$ 66,000,000.0	47,100,000											46,400,000
Fixed interest rate																				3.00%	3.36%
Principal amount of notes																				$ 66,400,000
Secured Debt
Debt Instrument [Line Items]
Secured borrowings										$ 12,600,000
Secured Debt | Receivables Purchase Agreement
Debt Instrument [Line Items]
Fixed interest rate										1.7771%
Proceeds from debt issuance	$ 100	$ 40	$ 70	$ 20	$ 20	$ 10	$ 10	$ 150					$ 160	$ 170	$ 190	$ 210	$ 280	$ 320	$ 420
Secured borrowings									$ 213,700,000	$ 309,100,000	$ 213,700,000											$ 215,500,000
Subordinated Debt | Subordinated debt maturing June 2029
Debt Instrument [Line Items]
Fixed interest rate									4.85%		4.85%
Principal amount of notes									$ 300,000,000.0		$ 300,000,000.0
Subordinated Debt | Subordinated debt maturing June 2024
Debt Instrument [Line Items]
Fixed interest rate												5.00%
Principal amount of notes												$ 140,000,000.0
Proceeds from debt issuance												$ 139,100,000