Securities - Securities In An Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Securities available-for-sale
Number of Securities | security	367	178
Available-for-Sale, Fair Value
Less Than 12 Months	$ 1,368,781	$ 682,644
12 Months or Longer	421,918	123,370
Total	1,790,699	806,014
Unrealized Losses
Less Than 12 Months	30,598	8,628
12 Months or Longer	19,269	1,585
Total	$ 49,867	$ 10,213
U.S. agency securities
Securities available-for-sale
Number of Securities | security	74	48
Available-for-Sale, Fair Value
Less Than 12 Months	$ 331,843	$ 253,841
12 Months or Longer	216,769	14,932
Total	548,612	268,773
Unrealized Losses
Less Than 12 Months	10,834	4,764
12 Months or Longer	10,354	212
Total	$ 21,188	$ 4,976
CMOs
Securities available-for-sale
Number of Securities | security	178	104
Available-for-Sale, Fair Value
Less Than 12 Months	$ 666,381	$ 349,853
12 Months or Longer	139,952	86,618
Total	806,333	436,471
Unrealized Losses
Less Than 12 Months	13,271	3,205
12 Months or Longer	7,580	1,118
Total	$ 20,851	$ 4,323
MBSs
Securities available-for-sale
Number of Securities | security	85	19
Available-for-Sale, Fair Value
Less Than 12 Months	$ 349,060	$ 69,838
12 Months or Longer	59,373	12,307
Total	408,433	82,145
Unrealized Losses
Less Than 12 Months	5,751	550
12 Months or Longer	1,175	90
Total	$ 6,926	$ 640
Municipal securities
Securities available-for-sale
Number of Securities | security	30	4
Available-for-Sale, Fair Value
Less Than 12 Months	$ 21,497	$ 1,012
12 Months or Longer	5,824	0
Total	27,321	1,012
Unrealized Losses
Less Than 12 Months	742	4
12 Months or Longer	160	0
Total	$ 902	$ 4
Corporate debt securities
Securities available-for-sale
Number of Securities | security		3
Available-for-Sale, Fair Value
Less Than 12 Months		$ 8,100
12 Months or Longer		9,513
Total		17,613
Unrealized Losses
Less Than 12 Months		105
12 Months or Longer		165
Total		$ 270