Investments - Schedule of Available-for-sale and Held-to-Maturity Securities (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Investment securities available-for-sale at fair value:
Amortized Cost	$ 1,319,395,000	$ 1,198,513,000
Unrealized Gains	34,135,000	45,805,000
Unrealized Losses	(14,122,000)	(625,000)
Fair Value	1,339,408,000	1,243,693,000
Investment securities held-to-maturity at amortized cost:
Amortized Cost	31,943,000	35,223,000
Unrealized Gains	688,000	719,000
Unrealized Losses	0	0
Fair Value	32,631,000	35,942,000
Equity securities at fair value:
Amortized Cost	39,708,000	41,452,000
Fair Value	39,708,000	41,452,000
U.S. government and agencies
Investment securities available-for-sale at fair value:
Amortized Cost	19,964,000	19,962,000
Unrealized Gains	650,000	1,022,000
Unrealized Losses	0	0
Fair Value	20,614,000	20,984,000
Government-sponsored entities
Investment securities available-for-sale at fair value:
Amortized Cost	137,866,000	142,985,000
Unrealized Gains	3,619,000	4,801,000
Unrealized Losses	0	0
Fair Value	141,485,000	147,786,000
Municipal bonds
Investment securities available-for-sale at fair value:
Amortized Cost	325,312,000	324,422,000
Unrealized Gains	17,668,000	22,177,000
Unrealized Losses	(585,000)	(11,000)
Fair Value	342,395,000	346,588,000
Mortgage-backed securities
Investment securities available-for-sale at fair value:
Amortized Cost	836,253,000	711,144,000
Unrealized Gains	12,198,000	17,805,000
Unrealized Losses	(13,537,000)	(614,000)
Fair Value	834,914,000	728,335,000
Investment securities held-to-maturity at amortized cost:
Amortized Cost	31,943,000	35,223,000
Unrealized Gains	688,000	719,000
Unrealized Losses	0	0
Fair Value	32,631,000	35,942,000
Money market mutual funds
Equity securities at fair value:
Amortized Cost	39,708,000	41,452,000
Fair Value	$ 39,708,000	$ 41,452,000