Goodwill and Other Intangible Assets - Summary of Goodwill and Other Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 480,391	$ 307,083
Other intangible assets, net	118,283	7,317
Total goodwill and intangible assets	598,674	314,400
Core Deposit
Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, net	106,634	301
Customer Lists
Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, net	10,241	6,992
Trademarks
Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, net	$ 1,408	$ 24