Debt and Equity Securities (Tables)

3 Months Ended

Mar. 31, 2017

Gross Unrealized Losses on Investments in Debt and Equity Securities

Gross unrealized losses on investments in debt and equity 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
March 31, 2017
Debt securities:
U.S. Treasury bonds	$	101,603	$	(1,999	)	$	—	$	—		$	101,603	$	(1,999	)
Municipal bonds		502,408		(20,827	)		19,279		(241	)		521,687		(21,068	)
Foreign government bonds		35,326		(995	)		356		(36	)		35,682		(1,031	)
Governmental agency bonds		148,314		(3,852	)		—		—			148,314		(3,852	)
Governmental agency mortgage-backed securities		1,116,770		(15,302	)		437,981		(6,726	)		1,554,751		(22,028	)
U.S. corporate debt securities		166,418		(3,810	)		18,903		(704	)		185,321		(4,514	)
Foreign corporate debt securities		48,175		(523	)		2,081		(142	)		50,256		(665	)
Total debt securities		2,119,014		(47,308	)		478,600		(7,849	)		2,597,614		(55,157	)
Equity securities		30,728		(739	)		61,083		(2,542	)		91,811		(3,281	)
Total	$	2,149,742	$	(48,047	)	$	539,683	$	(10,391	)	$	2,689,425	$	(58,438	)
December 31, 2016
Debt securities:
U.S. Treasury bonds	$	111,748	$	(4,466	)	$	—	$	—		$	111,748	$	(4,466	)
Municipal bonds		635,531		(26,317	)		16,485		(349	)		652,016		(26,666	)
Foreign government bonds		63,044		(2,371	)		324		(68	)		63,368		(2,439	)
Governmental agency bonds		148,112		(4,166	)		—		—			148,112		(4,166	)
Governmental agency mortgage-backed securities		1,295,790		(19,097	)		432,349		(7,695	)		1,728,139		(26,792	)
U.S. corporate debt securities		193,533		(4,560	)		24,499		(881	)		218,032		(5,441	)
Foreign corporate debt securities		78,658		(1,150	)		8,154		(340	)		86,812		(1,490	)
Total debt securities		2,526,416		(62,127	)		481,811		(9,333	)		3,008,227		(71,460	)
Equity securities		70,261		(1,173	)		59,019		(6,871	)		129,280		(8,044	)
Total	$	2,596,677	$	(63,300	)	$	540,830	$	(16,204	)	$	3,137,507	$	(79,504	)

Investments in Debt Securities

Investments in debt securities at March 31, 2017, 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	$	48,382	$	46,305	$	27,408	$	43,917	$	166,012
Estimated fair value	$	48,345	$	46,208	$	27,342	$	42,707	$	164,602
Municipal bonds
Amortized cost	$	53,829	$	326,434	$	246,075	$	395,999	$	1,022,337
Estimated fair value	$	53,912	$	328,993	$	246,199	$	380,982	$	1,010,086
Foreign government bonds
Amortized cost	$	14,386	$	98,459	$	7,630	$	16,288	$	136,763
Estimated fair value	$	14,483	$	98,871	$	7,695	$	15,373	$	136,422
Governmental agency bonds
Amortized cost	$	12,247	$	91,982	$	57,142	$	38,008	$	199,379
Estimated fair value	$	12,242	$	90,961	$	56,417	$	36,706	$	196,326
U.S. corporate debt securities
Amortized cost	$	29,515	$	283,343	$	313,183	$	68,104	$	694,145
Estimated fair value	$	29,588	$	286,375	$	314,884	$	67,989	$	698,836
Foreign corporate debt securities
Amortized cost	$	10,884	$	111,646	$	104,708	$	13,288	$	240,526
Estimated fair value	$	10,918	$	112,729	$	105,969	$	13,875	$	243,491
Total debt securities excluding mortgage-backed securities
Amortized cost	$	169,243	$	958,169	$	756,146	$	575,604	$	2,459,162
Estimated fair value	$	169,488	$	964,137	$	758,506	$	557,632	$	2,449,763
Total mortgage-backed securities
Amortized cost									$	2,152,814
Estimated fair value									$	2,134,329
Total debt securities
Amortized cost									$	4,611,976
Estimated fair value									$	4,584,092

Composition of Investment Portfolio by Credit Rating Agencies

The composition of the investment portfolio at March 31, 2017, by credit rating, is as follows:

	A- Ratings or higher			BBB+ to BBB- Ratings			Non-Investment Grade			Total
(in thousands, except percentages)	Estimated fair value		Percentage	Estimated fair value		Percentage	Estimated fair value		Percentage	Estimated fair value		Percentage
March 31, 2017
Debt securities:
U.S. Treasury bonds	$	164,602	100.0	$	—	—	$	—	—	$	164,602	100.0
Municipal bonds		948,633	93.9		56,451	5.6		5,002	0.5		1,010,086	100.0
Foreign government bonds		117,894	86.5		13,966	10.2		4,562	3.3		136,422	100.0
Governmental agency bonds		196,326	100.0		—	—		—	—		196,326	100.0
Governmental agency mortgage-backed securities		2,134,329	100.0		—	—		—	—		2,134,329	100.0
U.S. corporate debt securities		236,126	33.8		235,950	33.8		226,760	32.4		698,836	100.0
Foreign corporate debt securities		115,718	47.6		86,803	35.6		40,970	16.8		243,491	100.0
Total debt securities		3,913,628	85.4		393,170	8.6		277,294	6.0		4,584,092	100.0
Preferred stocks		—	—		10,048	58.1		7,251	41.9		17,299	100.0
Total	$	3,913,628	85.0	$	403,218	8.8	$	284,545	6.2	$	4,601,391	100.0

Composition of Investment Portfolio in Unrealized Loss Position by Credit Rating Agencies

The composition of the investment portfolio in an unrealized loss position at March 31, 2017, by credit rating, is as follows:

	A- Ratings or higher			BBB+ to BBB- Ratings			Non-Investment Grade			Total
(in thousands, except percentages)	Estimated fair value		Percentage	Estimated fair value		Percentage	Estimated fair value		Percentage	Estimated fair value		Percentage
March 31, 2017
Debt securities:
U.S. Treasury bonds	$	101,603	100.0	$	—	—	$	—	—	$	101,603	100.0
Municipal bonds		479,317	91.8		37,368	7.2		5,002	1.0		521,687	100.0
Foreign government bonds		19,233	53.9		13,010	36.5		3,439	9.6		35,682	100.0
Governmental agency bonds		148,314	100.0		—	—		—	—		148,314	100.0
Governmental agency mortgage-backed securities		1,554,751	100.0		—	—		—	—		1,554,751	100.0
U.S. corporate debt securities		64,826	35.0		75,090	40.5		45,405	24.5		185,321	100.0
Foreign corporate debt securities		19,805	39.4		23,102	46.0		7,349	14.6		50,256	100.0
Total debt securities		2,387,849	91.9		148,570	5.7		61,195	2.4		2,597,614	100.0
Preferred stocks		—	—		10,048	58.1		7,251	41.9		17,299	100.0
Total	$	2,387,849	91.3	$	158,618	6.1	$	68,446	2.6	$	2,614,913	100.0

Debt Securities

Investments Classified as Available-For-Sale

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
March 31, 2017
U.S. Treasury bonds	$	166,012	$	589	$	(1,999	)	$	164,602
Municipal bonds		1,022,337		8,817		(21,068	)		1,010,086
Foreign government bonds		136,763		690		(1,031	)		136,422
Governmental agency bonds		199,379		799		(3,852	)		196,326
Governmental agency mortgage-backed securities		2,152,814		3,543		(22,028	)		2,134,329
U.S. corporate debt securities		694,145		9,205		(4,514	)		698,836
Foreign corporate debt securities		240,526		3,630		(665	)		243,491
	$	4,611,976	$	27,273	$	(55,157	)	$	4,584,092
December 31, 2016
U.S. Treasury bonds	$	155,441	$	416	$	(4,466	)	$	151,391
Municipal bonds		1,004,659		6,340		(26,666	)		984,333
Foreign government bonds		141,887		600		(2,439	)		140,048
Governmental agency bonds		197,343		691		(4,166	)		193,868
Governmental agency mortgage-backed securities		2,187,482		2,983		(26,792	)		2,163,673
U.S. corporate debt securities		675,683		8,282		(5,441	)		678,524
Foreign corporate debt securities		240,526		2,490		(1,490	)		241,526
	$	4,603,021	$	21,802	$	(71,460	)	$	4,553,363

Equity securities

Investments Classified as Available-For-Sale

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

	Cost		Gross unrealized					Estimated fair value
(in thousands)	Cost		Gains		Losses			Estimated fair value
March 31, 2017
Preferred stocks	$	19,031	$	—	$	(1,732	)	$	17,299
Common stocks		362,743		39,130		(1,549	)		400,324
	$	381,774	$	39,130	$	(3,281	)	$	417,623
December 31, 2016
Preferred stocks	$	18,926	$	—	$	(3,344	)	$	15,582
Common stocks		367,169		26,034		(4,700	)		388,503
	$	386,095	$	26,034	$	(8,044	)	$	404,085