Investment Securities - Additional Information (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) security
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position (in security) | security	127		127		378
Fair value of investments held to maturity pledged as collateral	$ 1,300,000,000		$ 1,300,000,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years			6 years 7 months 6 days
Number of security positions in the securities available for sale portfolio in an unrealized loss position (in security) | security	294		294		545
Fair value of securities available for sale pledged as collateral	$ 1,100,000,000		$ 1,100,000,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years			6 years 8 months 12 days
Amortized cost	1,677,715,000		$ 1,677,715,000		$ 1,796,404,000
Other than temporary impairment losses recognized in earnings	2,900,000	$ 0		$ 0
Fair Value	1,679,350,000		1,679,350,000		1,749,544,000
Gross unrealized losses	$ 9,042,000		$ 9,042,000		$ 48,855,000
Single Issuer Trust Preferred Securities | Non-Rated
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position (in security) | security	4		4
US States and Political Subdivisions Debt Securities, Special Revenue Bonds, Impaired Securities
Investment Securities [Line Items]
Amortized cost	$ 680,000		$ 680,000
Fair Value	680,000		680,000
US States and Political Subdivisions Debt Securities, Special Revenue Bonds
Investment Securities [Line Items]
Amortized cost	306,500,000		306,500,000
Fair Value	308,500,000		308,500,000
Gross unrealized losses	$ 1,400,000		$ 1,400,000