Acquisitions - Consideration Paid and Allocation of Purchase Price to Net Assets Acquired (Details) - USD ($)	Jun. 16, 2017	Sep. 30, 2018	Dec. 31, 2017
Allocation of total consideration paid:
Goodwill		$ 1,807,121,000	$ 1,808,002,000
BNC Bancorp
Equity consideration:
Total equity consideration	$ 1,858,133,000
Non-equity consideration:
Cash paid to redeem common stock	129,000
Allocation of total consideration paid:
Fair value of net assets assumed including identifiable intangible assets	602,689,000
Goodwill	1,255,573,000
Total consideration paid	$ 1,858,262,000
BNC Bancorp | Common Stock
Equity consideration:
Common stock issued (in shares)	27,687,100
Total equity consideration	$ 1,858,133,000