Business Combinations - Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed at Date of Acquisition (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets acquired:
Bank owned life insurance		$ 218,673	$ 134,847
Liabilities assumed:
Goodwill recorded in the merger		$ 337,519	$ 150,501
Sun Bancorp, Inc.
Business Acquisition [Line Items]
Total Purchase Price:	$ 474,930
Assets acquired:
Cash and cash equivalents	68,632
Securities	254,522
Loans	1,517,947
Accrued interest receivable	5,621
Bank owned life insurance	85,238
Deferred tax asset	58,352
Other assets	42,530
Total assets acquired	2,044,739
Liabilities assumed:
Deposits	(1,616,073)
Borrowings	(127,747)
Other liabilities	(13,007)
Total liabilities assumed	(1,756,827)
Net assets acquired	287,912
Goodwill recorded in the merger	187,018
Sun Bancorp, Inc. | Book Value
Assets acquired:
Cash and cash equivalents	68,632
Securities	254,522
Loans	1,541,868
Accrued interest receivable	5,621
Bank owned life insurance	85,238
Deferred tax asset	55,710
Other assets	49,561
Core deposit intangible	0
Total assets acquired	2,061,152
Liabilities assumed:
Deposits	(1,614,910)
Borrowings	(142,567)
Other liabilities	(14,372)
Total liabilities assumed	(1,771,849)
Net assets acquired	289,303
Purchase Accounting Adjustments | Sun Bancorp, Inc.
Assets acquired:
Cash and cash equivalents	0
Securities	0
Loans	(23,921)
Accrued interest receivable	0
Bank owned life insurance	0
Deferred tax asset	2,642
Other assets	(7,031)
Core deposit intangible	11,897
Total assets acquired	(16,413)
Liabilities assumed:
Deposits	(1,163)
Borrowings	14,820
Other liabilities	1,365
Total liabilities assumed	15,022
Net assets acquired	$ (1,391)