Loans Receivable, Net - Summary of Loans Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Summary of Loans Receivable
Loans receivable	$ 11,618,731		$ 9,512,810
Allowance for credit losses	(164,552)	$ (162,509)	(124,490)	$ (125,535)	$ (129,054)	$ (131,239)
Loans receivable, net	11,454,179		9,388,320
Net deferred origination (fees) costs included in loans receivable	(38,712)		(6,964)
Net purchase accounting (discounts) premiums included in loans receivable	(18,063)		(21,574)
Accrued interest receivable on loans	65,806		40,962
Residential Real Estate
Summary of Loans Receivable
Loans receivable	862,614		926,388
Allowance for credit losses	(9,805)	(9,986)	(10,111)	(10,237)	(10,695)	(10,631)
Commercial Real Estate
Summary of Loans Receivable
Loans receivable	6,201,817		5,579,307
Allowance for credit losses	(94,397)	(89,104)	(69,496)	(69,658)	(72,447)	(72,448)
Other Commercial
Summary of Loans Receivable
Loans receivable	3,593,322		2,094,254
Allowance for credit losses	(48,753)	(48,838)	(36,129)	(36,858)	(36,259)	(38,160)
Home Equity
Summary of Loans Receivable
Loans receivable	646,850		617,201
Allowance for credit losses	(7,430)	(9,962)	(4,937)	(5,041)	(5,801)	(5,811)
Other Consumer
Summary of Loans Receivable
Loans receivable	314,128		295,660
Allowance for credit losses	$ (4,167)	$ (4,619)	$ (3,817)	$ (3,741)	$ (3,852)	$ (4,189)