FHLB Advances, Other Borrowings and Subordinated Notes (Narrative) (Details) $ in Millions	1 Months Ended		3 Months Ended
	Dec. 31, 2017 CAD ($)	Dec. 31, 2015 CAD ($)	Mar. 31, 2018 USD ($) Rate	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CAD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2014 CAD ($)	Dec. 15, 2014 USD ($)
Debt Instrument [Line Items]
Notes payable			$ 33,727,000	$ 41,222,000		$ 48,702,000
Loan agreement with unaffiliated banks			150,000,000
Short-term borrowings			17,977,000	17,209,000		39,246,000
Other			48,742,000	49,131,000		17,949,000
Secured borrowings			146,646,000	158,561,000		132,890,000
Subordinated notes			$ 139,111,000	139,088,000		138,993,000
Base Rate Loan | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate			0.50%
Base Rate Loan | Eurodollar Rate
Debt Instrument [Line Items]
Basis spread on variable rate			1.00%
Term Facility
Debt Instrument [Line Items]
Notes payable			$ 33,700,000	41,200,000		48,700,000		$ 75,000,000
Term Facility | Base Rate Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate			0.75%
Term Facility | Eurodollar Rate Loan | Eurodollar Rate
Debt Instrument [Line Items]
Basis spread on variable rate			1.75%
Revolving Credit Facility
Debt Instrument [Line Items]
Notes payable			$ 0	0		0
Maximum borrowing capacity								$ 75,000,000.0
Commitment fee (as a percent) | Rate			0.20%
Revolving Credit Facility | Base Rate Loan | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate			0.50%
Revolving Credit Facility | Eurodollar Rate Loan | Eurodollar Rate
Debt Instrument [Line Items]
Basis spread on variable rate			1.50%
Securities sold under repurchase agreements
Debt Instrument [Line Items]
Securities sold under agreements to repurchase			$ 18,000,000	17,200,000		39,200,000
Pledged financial instruments			43,400,000
Fixed Rate Promissory Note
Debt Instrument [Line Items]
Other			$ 48,700,000	49,000,000		17,600,000
Fixed rate (as a percent)			3.36%
Non Recourse Debt
Debt Instrument [Line Items]
Other			$ 75,000	151,000		374,000
Secured Debt
Debt Instrument [Line Items]
Secured borrowings			$ 15,000,000
Secured Debt | Receivables Purchase Agreement
Debt Instrument [Line Items]
Fixed rate (as a percent)			2.4253%
Secured borrowings		$ 160	$ 131,700,000	$ 135,100,000	$ 170	$ 120,100,000	$ 150
Additional amount paid by third party	$ 10	$ 10
Subordinated Debt
Debt Instrument [Line Items]
Fixed rate (as a percent)			5.00%