Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 1,084,665,000		$ 1,084,665,000
Goodwill impairment	0	$ 0
Amortization of other intangible assets	$ 4,311,000	4,293,000
Core Deposits
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	8 years 2 months 12 days
Other
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	7 years 7 months 6 days
Core Deposits and Other
Finite-Lived Intangible Assets [Line Items]
Impairment of core deposits and other intangibles	$ 0	$ 0