Investment Securities - Additional Information (Detail)	3 Months Ended
Mar. 31, 2019 USD ($) Security	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)
Investment [Line Items]
Held-to-Maturity, Unrecognized Losses	$ 3,368,000	$ 17,211,000
OTTI losses on securities	$ 0		$ 0
Number of securities in security portfolio \| Security	2,057
Number of securities in unrealized loss position \| Security	532
Total investment securities - available-for-sale	$ 4,569,772,000	4,123,416,000	3,219,863,000
Unrealized losses	36,582,000	70,573,000
Securities portfolio at fair value	6,235,000	5,582,000	5,569,000
Gains on equity securities	200,000		100,000
Impairments on equity securities without readily determinable fair value	0		0
Downward adjustments on equity securities without readily determinable fair value	0		0
Other Asstes [Member]
Investment [Line Items]
Equity securities without readily determinable fair value	$ 76,600,000	79,200,000
Pooled Trust Preferred Securities [Member]
Investment [Line Items]
Number of pooled trust preferred securities \| Security	2
Total investment securities - available-for-sale	$ 8,123,000	8,495,000
Unrealized losses	5,727,000	5,366,000
OTTI losses on securities		0	$ 0
Held-to-maturity Securities [Member]
Investment [Line Items]
Held-to-Maturity, Unrecognized Losses	$ 3,100,000	$ 10,700,000

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
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