Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) Subsidiary	Dec. 31, 2018 USD ($)
Significant Of Accounting Policies [Line Items]
Investment securities - AFS, at fair value; amortized cost of $3,265,546 at March 31, 2019 and $3,339,888 at December 31, 2018 | $	$ 3,244,247	$ 3,276,988
Number Of Wholly Owned Subsidiaries Non Bank Subsidiaries	2
Number Of Unconsolidated Subsidiaries	8