Securities - Securities Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,225,285	$ 3,043,480
Gross Unrealized Gains	37,490	63,141
Gross Unrealized Losses	(49,867)	(10,213)
Fair Value	3,212,908	3,096,408
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,853	12,071
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(392)	(385)
Fair Value	10,461
Allowance for securities held-to-maturity	(220)	(220)
Securities held-to-maturity, at amortized cost, net	10,633	12,071
Fair value, net of allowance	10,241	11,686
Equity securities	114,848	76,404
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	12,001
Gross Unrealized Gains	0	50
Gross Unrealized Losses	0	0
Fair Value	0	12,051
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	675,866	654,321
Gross Unrealized Gains	1,434	3,129
Gross Unrealized Losses	(21,188)	(4,976)
Fair Value	656,112	652,474
Collateralized mortgage obligations ("CMOs")
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,304,762	1,415,312
Gross Unrealized Gains	11,633	27,529
Gross Unrealized Losses	(20,851)	(4,323)
Fair Value	1,295,544	1,438,518
Other mortgage-backed securities ("MBSs")
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	854,852	566,830
Gross Unrealized Gains	8,170	14,650
Gross Unrealized Losses	(6,926)	(640)
Fair Value	856,096	580,840
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	216,744	224,446
Gross Unrealized Gains	8,776	11,573
Gross Unrealized Losses	(902)	(4)
Fair Value	224,618	236,015
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,853	12,291
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(392)	(385)
Fair Value	10,461	11,906
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	173,061	170,570
Gross Unrealized Gains	7,477	6,210
Gross Unrealized Losses	0	(270)
Fair Value	$ 180,538	$ 176,510

Debt Securities, Held-to-maturity, Fair Value, Net Of Allowance For Credit Losses

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Debt Securities, Held-To-Maturity, Net Of Allowance For Credit Losses

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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