Marketable Securities - Available For Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized cost
Residential mortgage-backed securities	$ 749,703	$ 815,495
Gross unrealized holding gains
Residential mortgage-backed securities, gross unrealized holding gains	16,923	7,351
Gross unrealized holding losses
Residential mortgage-backed securities, gross unrealized holding losses	(1,047)	(2,945)
Fair value
Securities available-for-sale	765,579	819,901
U.S. government and agencies
Amortized cost
Due in one year through five years		14,951
Gross unrealized holding gains
Due in one year through five years		40
Gross unrealized holding losses
Due in one year through five years		0
Fair value
Due in one year through five years		14,991
Debt issued by government sponsored enterprises:
Amortized cost
Due in less than one year	50,761	50,777
Due in one year through five years	25,227	50,229
Due in five years through ten years	3,411
Due after ten years		3,716
Gross unrealized holding gains
Due in less than one year	475	345
Due in one year through five years	284	0
Due in five years through ten years	114
Due after ten years		53
Gross unrealized holding losses
Due in less than one year	0	0
Due in one year through five years	0	(227)
Due in five years through ten years	(103)
Due after ten years		(109)
Fair value
Due in less than one year	51,236	51,122
Due in one year through five years	25,511	50,002
Due in five years through ten years	3,422
Due after ten years		3,660
Municipal securities
Amortized cost
Due in less than one year	812	809
Due in one year through five years	2,897	2,891
Due in five years through ten years	8,903	10,155
Due after ten years	31,400	11,695
Gross unrealized holding gains
Due in less than one year	3	4
Due in one year through five years	68	79
Due in five years through ten years	178	148
Due after ten years	436	267
Gross unrealized holding losses
Due in less than one year	0	0
Due in one year through five years	0	0
Due in five years through ten years	0	0
Due after ten years	0	0
Fair value
Due in less than one year	815	813
Due in one year through five years	2,965	2,970
Due in five years through ten years	9,081	10,303
Due after ten years	31,836	11,962
Corporate debt securities
Amortized cost
Due in five years through ten years		919
Gross unrealized holding gains
Due in five years through ten years		0
Gross unrealized holding losses
Due in five years through ten years		0
Fair value
Due in five years through ten years		919
Residential mortgage-backed securities
Amortized cost
Residential mortgage-backed securities	626,292	669,353
Gross unrealized holding gains
Residential mortgage-backed securities, gross unrealized holding gains	15,365	6,415
Gross unrealized holding losses
Residential mortgage-backed securities, gross unrealized holding losses	(944)	(2,609)
Fair value
Securities available-for-sale	640,713	673,159
Fixed rate | Pass-through
Amortized cost
Residential mortgage-backed securities	130,729	142,421
Gross unrealized holding gains
Residential mortgage-backed securities, gross unrealized holding gains	4,453	1,941
Gross unrealized holding losses
Residential mortgage-backed securities, gross unrealized holding losses	(10)	(881)
Fair value
Securities available-for-sale	135,172	143,481
Fixed rate | Agency CMOs
Amortized cost
Residential mortgage-backed securities	423,625	452,256
Gross unrealized holding gains
Residential mortgage-backed securities, gross unrealized holding gains	10,447	3,518
Gross unrealized holding losses
Residential mortgage-backed securities, gross unrealized holding losses	(60)	(1,606)
Fair value
Securities available-for-sale	434,012	454,168
Variable rate | Pass-through
Amortized cost
Residential mortgage-backed securities	18,025	18,933
Gross unrealized holding gains
Residential mortgage-backed securities, gross unrealized holding gains	403	749
Gross unrealized holding losses
Residential mortgage-backed securities, gross unrealized holding losses	(8)	(4)
Fair value
Securities available-for-sale	18,420	19,678
Variable rate | Agency CMOs
Amortized cost
Residential mortgage-backed securities	53,913	55,743
Gross unrealized holding gains
Residential mortgage-backed securities, gross unrealized holding gains	62	207
Gross unrealized holding losses
Residential mortgage-backed securities, gross unrealized holding losses	(866)	(118)
Fair value
Securities available-for-sale	$ 53,109	$ 55,832