Business Combinations - Summary of Estimated Fair Values of Assets Purchased and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Apr. 07, 2017	Dec. 31, 2016	Dec. 31, 2015
Liabilities:
Goodwill	$ 379,627		$ 366,156	$ 366,156
Reliance [Member]
Assets:
Cash and due from banks		$ 5,013
Federal funds sold and securities purchased under reverse repurchase agreements		6,900
Securities		54,843
Acquired loans		117,447
Premises and equipment, net		3,700
Identifiable intangible assets		1,850
Other real estate		475
Other assets		6,037
Total Assets		196,265
Liabilities:
Deposits		166,158
Other borrowings		17,469
Other liabilities		1,322
Total Liabilities		184,949
Net identified assets acquired at fair value		11,316
Goodwill	$ 13,500	13,471
Total consideration paid		$ 24,787