Loans, Allowance for Loan Losses and Allowance for Unfunded Credit Commitments - Allowance for Credit Losses: Unfunded Credit Commitments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss, beginning balance	$ 304,924	$ 280,903
(Reduction of) provision for credit losses	248,901	25,821
Foreign currency translation adjustments	(1,185)	1,002
Allowance for credit loss, ending balance	548,963	300,151
Cumulative adjustment for the adoption of amendment
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss, beginning balance	25,464
Unfunded Credit Commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss, beginning balance	67,656	55,183
(Reduction of) provision for credit losses	(5,477)	2,730
Foreign currency translation adjustments	(315)	57
Allowance for credit loss, ending balance	84,690	57,970
Unfunded Credit Commitments | Cumulative adjustment for the adoption of amendment
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss, beginning balance	$ 22,826	$ 0