Variable Interest Entities - Additional Information (Details) $ in Thousands	Dec. 31, 2017 USD ($) entity	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Variable Interest Entity [Line Items]
Amortization method qualified affordable housing project investments	$ 174,214	$ 112,447
Qualified Affordable Housing Project Investments, Commitment	100,891	58,095
Total assets	(51,214,467)	(44,683,660)
Total equity	$ (4,319,415)	(3,777,037)	$ (3,333,231)	$ (4,051,734)
Number of consolidated entities | entity	4
Maximum Exposure to Loss in Unconsolidated VIEs	$ 346,097	314,810
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Total assets	(346,097)	(314,810)
Accrued expenses and other liabilities	100,891	58,095
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total assets	(197,601)	(207,903)
Accrued expenses and other liabilities	990	$ 517
Maximum Exposure to Loss in Unconsolidated VIEs	$ 196,600