FHLB Advances, Other Borrowings and Subordinated Notes (Narrative) (Details) $ in Millions	1 Months Ended					3 Months Ended	6 Months Ended		24 Months Ended	48 Months Ended	54 Months Ended	62 Months Ended
	Feb. 28, 2019 CAD ($)	Jun. 30, 2018 CAD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2015 CAD ($)	Dec. 31, 2014 CAD ($)	Jun. 30, 2019 USD ($) building	Jun. 30, 2019 USD ($) building Rate	Jun. 30, 2018 USD ($)	Dec. 31, 2015 CAD ($)	Dec. 31, 2017 CAD ($)	Jun. 30, 2018 CAD ($)	Feb. 28, 2019 CAD ($)	Dec. 31, 2018 USD ($)	Sep. 18, 2018 USD ($)	Dec. 15, 2014 USD ($)
Debt Instrument [Line Items]
Notes payable						$ 133,776,000	$ 133,776,000	$ 29,982,000					$ 144,461,000	$ 150,000,000.0	$ 150,000,000.0
Short-term borrowings						10,182,000	10,182,000	21,437,000					50,593,000
Other borrowings						47,072,000	47,072,000	48,369,000					47,722,000
Secured borrowings						227,027,000	227,027,000	155,913,000					151,079,000
Subordinated notes						436,021,000	436,021,000	139,148,000					139,210,000
Proceeds from the issuance of subordinated notes, net							296,741,000	0
Revolving Credit Facility
Debt Instrument [Line Items]
Notes payable														50,000,000.0	75,000,000.0
Proceeds from credit facility						35,000,000.0
Amount outstanding						0	0
Term Facility
Debt Instrument [Line Items]
Notes payable						133,800,000	133,800,000	30,000,000.0						150,000,000.0	$ 75,000,000.0
Subordinated debt maturing June 2029
Debt Instrument [Line Items]
Proceeds from the issuance of subordinated notes, net						296,700,000
Subordinated debt maturing June 2024
Debt Instrument [Line Items]
Subordinated notes						139,300,000	$ 139,300,000
Base Rate Loan | Base Rate | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate							0.50%
Base Rate Loan | Base Rate | Term Facility
Debt Instrument [Line Items]
Basis spread on variable rate							0.75%
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) | Revolving Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate							1.25%
Eurodollar Rate Loan | London Interbank Offered Rate (LIBOR) | Term Facility
Debt Instrument [Line Items]
Basis spread on variable rate							1.25%
Line of Credit | Credit Agreement
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	21,400,000					50,600,000
Pledged financial instruments						$ 22,300,000	$ 22,300,000
Fixed Rate Promissory Note
Debt Instrument [Line Items]
Number of properties securing debt | building						2	2
Other borrowings						$ 47,100,000	$ 47,100,000	48,400,000					47,700,000
Fixed interest rate						3.36%	3.36%
Secured Debt
Debt Instrument [Line Items]
Secured borrowings						$ 13,300,000	$ 13,300,000
Secured Debt | Receivables Purchase Agreement
Debt Instrument [Line Items]
Fixed interest rate						2.7093%	2.7093%
Proceeds from debt issuance	$ 20	$ 20	$ 10	$ 10	$ 150				$ 160	$ 170	$ 190	$ 210
Secured borrowings						$ 213,700,000	$ 213,700,000	$ 144,600,000					$ 139,300,000
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%	5.00%