Variable Interest Entities - Carrying Amounts and Classification of Significant Variable Interests (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	[1]
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 2,923,075	$ 2,545,750	$ 1,503,257	$ 1,811,014
Non-marketable and other securities	651,053	622,552
Accrued interest receivable and other assets	876,246	672,688
Total assets	51,214,467	44,683,660
Other liabilities	911,755	618,383
Total liabilities	46,895,052	40,906,623
Maximum Exposure to Loss in Unconsolidated VIEs	346,097	314,810
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	6,674	11,469
Non-marketable and other securities	190,562	196,140
Accrued interest receivable and other assets	365	294
Total assets	197,601	207,903
Accrued expenses and other liabilities	990	517
Total liabilities	990	517
Maximum Exposure to Loss in Unconsolidated VIEs	196,600
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	0	0
Non-marketable and other securities	346,097	314,810
Accrued interest receivable and other assets	0	0
Total assets	346,097	314,810
Accrued expenses and other liabilities	100,891	58,095
Total liabilities	$ 100,891	$ 58,095

[1] Cash and cash equivalents at December 31, 2014 included $15.0 million recognized in assets held-for-sale in conjunction with the SVBIF sale transaction. On April 13, 2015 we received net proceeds of $39.3 million consisting of the sales price of $48.6 million less $9.3 million of cash and cash equivalents held by SVBIF that were sold.