Investment Securities Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Schedule of Investments [Line Items]
Amortized cost	$ 2,548,261		$ 2,548,261
Available-for-sale Securities, Fair Value Disclosure	2,644,299		2,644,299		$ 2,497,537
HTM, at amortized cost	330,514		330,514		369,841
HTM securities	354,109		354,109
Prepayment penalty on FHLB advances	2,878	$ 0	2,878	$ 0
Debt Securities [Member]
Schedule of Investments [Line Items]
HTM, at amortized cost	79,000		79,000
HTM securities	82,000		82,000
Debt Securities, Held-to-maturity, Sold, Realized Gain (Loss)	3,000
Prepayment penalty on FHLB advances	2,900
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized cost	156,152		156,152
Available-for-sale Securities, Fair Value Disclosure	160,868		160,868
HTM, at amortized cost	330,514		330,514		369,841
HTM securities	354,109		354,109		383,705
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Amortized cost	852,617		852,617
Available-for-sale Securities, Fair Value Disclosure	893,682		893,682
Collateral Pledged [Member]
Schedule of Investments [Line Items]
Securities pledged as collateral	$ 468,800		$ 468,800		$ 462,600