Debt and Equity Securities (Tables)

6 Months Ended

Jun. 30, 2019

Investments in debt securities, classified as available-for-sale, are as follows:

(in thousands)	Amortized cost		Gross unrealized					Estimated fair value
(in thousands)	Amortized cost		Gains		Losses			Estimated fair value
June 30, 2019
U.S. Treasury bonds	$	243,585	$	1,746	$	(49	)	$	245,282
Municipal bonds		1,048,405		38,331		(205	)		1,086,531
Foreign government bonds		150,800		1,904		(150	)		152,554
Governmental agency bonds		391,720		5,958		(514	)		397,164
Governmental agency mortgage-backed securities		3,259,857		42,378		(9,940	)		3,292,295
U.S. corporate debt securities		526,138		15,896		(1,051	)		540,983
Foreign corporate debt securities		279,122		6,774		(783	)		285,113
	$	5,899,627	$	112,987	$	(12,692	)	$	5,999,922
December 31, 2018
U.S. Treasury bonds	$	162,904	$	741	$	(1,139	)	$	162,506
Municipal bonds		1,050,134		7,210		(12,309	)		1,045,035
Foreign government bonds		158,885		571		(2,159	)		157,297
Governmental agency bonds		319,115		1,145		(4,093	)		316,167
Governmental agency mortgage-backed securities		3,219,585		12,030		(29,016	)		3,202,599
U.S. corporate debt securities		575,646		1,113		(15,499	)		561,260
Foreign corporate debt securities		274,881		551		(6,485	)		268,947
	$	5,761,150	$	23,361	$	(70,700	)	$	5,713,811

Gross unrealized losses on investments in debt securities are as follows:

	Less than 12 months					12 months or longer					Total
(in thousands)	Estimated fair value		Unrealized losses			Estimated fair value		Unrealized losses			Estimated fair value		Unrealized losses
June 30, 2019
U.S. Treasury bonds	$	8,921	$	(11	)	$	14,863	$	(38	)	$	23,784	$	(49	)
Municipal bonds		9,029		(46	)		59,364		(159	)		68,393		(205	)
Foreign government bonds		47,048		(79	)		13,020		(71	)		60,068		(150	)
Governmental agency bonds		15,282		(67	)		45,817		(447	)		61,099		(514	)
Governmental agency mortgage-backed securities		466,134		(1,963	)		891,182		(7,977	)		1,357,316		(9,940	)
U.S. corporate debt securities		66,367		(575	)		48,940		(476	)		115,307		(1,051	)
Foreign corporate debt securities		25,369		(400	)		29,905		(383	)		55,274		(783	)
	$	638,150	$	(3,141	)	$	1,103,091	$	(9,551	)	$	1,741,241	$	(12,692	)
December 31, 2018
U.S. Treasury bonds	$	19,749	$	(85	)	$	55,615	$	(1,054	)	$	75,364	$	(1,139	)
Municipal bonds		172,387		(1,772	)		369,139		(10,537	)		541,526		(12,309	)
Foreign government bonds		23,654		(1,037	)		42,119		(1,122	)		65,773		(2,159	)
Governmental agency bonds		56,270		(748	)		90,631		(3,345	)		146,901		(4,093	)
Governmental agency mortgage-backed securities		850,459		(6,955	)		982,610		(22,061	)		1,833,069		(29,016	)
U.S. corporate debt securities		374,473		(10,537	)		109,844		(4,962	)		484,317		(15,499	)
Foreign corporate debt securities		175,762		(4,575	)		50,802		(1,910	)		226,564		(6,485	)
	$	1,672,754	$	(25,709	)	$	1,700,760	$	(44,991	)	$	3,373,514	$	(70,700	)

Investments in debt securities at June 30, 2019, by contractual maturities, are as follows:

(in thousands)	Due in one year or less		Due after one through five years		Due after five through ten years		Due after ten years		Total
U.S. Treasury bonds
Amortized cost	$	173,833	$	63,118	$	109	$	6,525	$	243,585
Estimated fair value	$	173,928	$	63,656	$	138	$	7,560	$	245,282
Municipal bonds
Amortized cost	$	70,793	$	164,852	$	256,433	$	556,327	$	1,048,405
Estimated fair value	$	71,018	$	166,972	$	266,762	$	581,779	$	1,086,531
Foreign government bonds
Amortized cost	$	25,100	$	98,871	$	18,513	$	8,316	$	150,800
Estimated fair value	$	25,036	$	99,847	$	19,164	$	8,507	$	152,554
Governmental agency bonds
Amortized cost	$	27,209	$	120,988	$	158,143	$	85,380	$	391,720
Estimated fair value	$	27,196	$	121,778	$	161,447	$	86,743	$	397,164
U.S. corporate debt securities
Amortized cost	$	42,651	$	274,338	$	183,178	$	25,971	$	526,138
Estimated fair value	$	42,640	$	280,571	$	189,542	$	28,230	$	540,983
Foreign corporate debt securities
Amortized cost	$	24,110	$	172,822	$	73,892	$	8,298	$	279,122
Estimated fair value	$	24,134	$	175,232	$	76,848	$	8,899	$	285,113
Total debt securities excluding mortgage-backed securities
Amortized cost	$	363,696	$	894,989	$	690,268	$	690,817	$	2,639,770
Estimated fair value	$	363,952	$	908,056	$	713,901	$	721,718	$	2,707,627
Total mortgage-backed securities
Amortized cost									$	3,259,857
Estimated fair value									$	3,292,295
Total debt securities
Amortized cost									$	5,899,627
Estimated fair value									$	5,999,922

Investments in equity securities are as follows:

The composition of the investment portfolio at June 30, 2019, by credit rating, is as follows:

	A- or higher				BBB+ to BBB-				Non-Investment Grade				Total
(in thousands, except percentages)	Estimated fair value		Percentage		Estimated fair value		Percentage		Estimated fair value		Percentage		Estimated fair value		Percentage
Debt securities:
U.S. Treasury bonds	$	245,282		100.0	$	—		—	$	—		—	$	245,282		100.0
Municipal bonds		1,045,937		96.3		39,214		3.6		1,380		0.1		1,086,531		100.0
Foreign government bonds		133,639		87.6		13,453		8.8		5,462		3.6		152,554		100.0
Governmental agency bonds		397,164		100.0		—		—		—		—		397,164		100.0
Governmental agency mortgage-backed securities		3,292,295		100.0		—		—		—		—		3,292,295		100.0
U.S. corporate debt securities		250,349		46.3		201,802		37.3		88,832		16.4		540,983		100.0
Foreign corporate debt securities		120,447		42.2		141,873		49.8		22,793		8.0		285,113		100.0
Total debt securities		5,485,113		91.4		396,342		6.6		118,467		2.0		5,999,922		100.0
Preferred stocks		47		0.3		12,230		91.0		1,163		8.7		13,440		100.0
Total	$	5,485,160		91.2	$	408,572		6.8	$	119,630		2.0	$	6,013,362		100.0

The composition of the debt securities portfolio in an unrealized loss position at June 30, 2019, by credit rating, is as follows:

	A- or higher				BBB+ to BBB-				Non-Investment Grade				Total
(in thousands, except percentages)	Estimated fair value		Percentage		Estimated fair value		Percentage		Estimated fair value		Percentage		Estimated fair value		Percentage
U.S. Treasury bonds	$	23,784		100.0	$	—		—	$	—		—	$	23,784		100.0
Municipal bonds		68,393		100.0		—		—		—		—		68,393		100.0
Foreign government bonds		58,156		96.8		—		—		1,912		3.2		60,068		100.0
Governmental agency bonds		61,099		100.0		—		—		—		—		61,099		100.0
Governmental agency mortgage-backed securities		1,357,316		100.0		—		—		—		—		1,357,316		100.0
U.S. corporate debt securities		38,572		33.4		24,435		21.2		52,300		45.4		115,307		100.0
Foreign corporate debt securities		23,366		42.3		19,679		35.6		12,229		22.1		55,274		100.0
Total	$	1,630,686		93.7	$	44,114		2.5	$	66,441		3.8	$	1,741,241		100.0