Business Combinations - Summary of Assets Acquired and Liabilities Assumed and Their Initial Fair Value Estimates (Detail) - USD ($) $ in Thousands	Jan. 31, 2019	Jan. 31, 2018	Sep. 30, 2019	Dec. 31, 2018
Assets acquired:
Bank Owned Life Insurance			$ 236,190	$ 222,482
Liabilities Assumed
Goodwill recorded in the merger			$ 374,537	$ 338,442
Sun Bancorp, Inc.
Business Acquisition [Line Items]
Total consideration paid		$ 474,930
Assets acquired:
Cash and cash equivalents		68,632
Securities		254,522
Loans		1,517,345
Accrued interest receivable		5,621
Bank Owned Life Insurance		85,238
Deferred tax asset		57,597
Other assets		43,202
Core deposit intangible		11,897
Total assets acquired		2,044,054
Liabilities Assumed
Deposits		(1,616,073)
Borrowings		(127,727)
Other liabilities		(13,242)
Total liabilities assumed		(1,757,042)
Net assets acquired		287,012
Goodwill recorded in the merger		$ 187,918
Capital Bank
Business Acquisition [Line Items]
Total consideration paid	$ 76,834
Assets acquired:
Cash and cash equivalents	59,748
Securities	103,775
Loans	307,778
Accrued interest receivable	1,390
Bank Owned Life Insurance	10,460
Deferred tax asset	3,829
Other assets	5,107
Core deposit intangible	2,662
Total assets acquired	494,749
Liabilities Assumed
Deposits	(449,018)
Other liabilities	(5,015)
Total liabilities assumed	(454,033)
Net assets acquired	40,716
Goodwill recorded in the merger	$ 36,118