Investment Securities (Tables)

3 Months Ended

Mar. 31, 2017

Investments [Abstract]

Summary of Available-for-Sale Investment Securities

The amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities available for sale at March 31, 2017 and December 31, 2016 are summarized below.

	March 31, 2017
(in thousands)	Amortized Cost		Gross Unrealized Gains	Gross Unrealized Losses		Fair Value
U.S. Treasury securities	$	83,441	—	(550	)	82,891
U.S. Government agency securities	12,089		342	—		12,431
Mortgage-backed securities issued by U.S. Government agencies	166,794		787	(1,302	)	166,279
Mortgage-backed securities issued by U.S. Government sponsored enterprises	2,837,359		3,779	(38,594	)	2,802,544
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	710,188		12	(13,308	)	696,892
State and municipal securities	1,800		1	—		1,801
Other investments	20,263		144	(303	)	20,104
Total investment securities available for sale	$	3,831,934	5,065	(54,057	)	3,782,942
	December 31, 2016
(in thousands)	Amortized Cost		Gross Unrealized Gains	Gross Unrealized Losses		Fair Value
U.S. Treasury securities	$	108,221	225	(644	)	107,802
U.S. Government agency securities	12,727		266	—		12,993
Mortgage-backed securities issued by U.S. Government agencies	174,440		1,116	(1,354	)	174,202
Mortgage-backed securities issued by U.S. Government sponsored enterprises	2,543,495		5,416	(42,571	)	2,506,340
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	905,789		1,214	(16,561	)	890,442
State and municipal securities	2,780		14	—		2,794
Equity securities	919		2,863	—		3,782
Other investments	20,247		—	(407	)	19,840
Total investment securities available for sale	$	3,768,618	11,114	(61,537	)	3,718,195

Schedule of Unrealized Loss on Investments

Gross unrealized losses on investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at March 31, 2017 and December 31, 2016 are presented below.

	March 31, 2017
	Less than 12 Months			12 Months or Longer		Total
(in thousands)	Fair Value		Gross Unrealized Losses	Fair Value	Gross Unrealized Losses	Fair Value	Gross Unrealized Losses
U.S. Treasury securities	$	64,134	550	—	—	64,134	550
Mortgage-backed securities issued by U.S. Government agencies	123,299		1,185	3,497	117	126,796	1,302
Mortgage-backed securities issued by U.S. Government sponsored enterprises	2,155,464		38,594	—	—	2,155,464	38,594
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	641,126		12,420	23,723	888	664,849	13,308
Other investments	—		—	4,959	303	4,959	303
Total	$	2,984,023	52,749	32,179	1,308	3,016,202	54,057
	December 31, 2016
	Less than 12 Months			12 Months or Longer		Total
(in thousands)	Fair Value		Gross Unrealized Losses	Fair Value	Gross Unrealized Losses	Fair Value	Gross Unrealized Losses
U.S. Treasury securities	$	64,023	644	—	—	64,023	644
Mortgage-backed securities issued by U.S. Government agencies	128,121		1,240	3,626	114	131,747	1,354
Mortgage-backed securities issued by U.S. Government sponsored enterprises	2,123,181		42,571	—	—	2,123,181	42,571
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	682,492		15,653	24,801	908	707,293	16,561
Other investments	14,952		48	4,888	359	19,840	407
Total	$	3,012,769	60,156	33,315	1,381	3,046,084	61,537

Amortized Cost and Estimated Fair Value by Contractual Maturity of Investment Securities Available-for-Sale

For purposes of the maturity table, mortgage-backed securities and CMOs, which are not due at a single maturity date, have been classified based on the final contractual maturity date.

	Distribution of Maturities at March 31, 2017
(in thousands)	Within One Year		1 to 5 Years	5 to 10 Years	More Than 10 Years	No Stated Maturity	Total
Amortized Cost
U.S. Treasury securities	$	18,756	64,685	—	—	—	83,441
U.S. Government agency securities	999		5,613	5,477	—	—	12,089
Mortgage-backed securities issued by U.S. Government agencies	—		—	33,513	133,281	—	166,794
Mortgage-backed securities issued by U.S. Government sponsored enterprises	93		1,603	570,250	2,265,413	—	2,837,359
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	—		—	—	710,188	—	710,188
State and municipal securities	1,620		180	—	—	—	1,800
Other investments	—		—	15,000	2,000	3,263	20,263
Total amortized cost	$	21,468	72,081	624,240	3,110,882	3,263	3,831,934
Fair Value
U.S. Treasury securities	$	18,756	64,135	—	—	—	82,891
U.S. Government agency securities	1,012		5,744	5,675	—	—	12,431
Mortgage-backed securities issued by U.S. Government agencies	—		—	33,728	132,551	—	166,279
Mortgage-backed securities issued by U.S. Government sponsored enterprises	96		1,700	565,770	2,234,978	—	2,802,544
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	—		—	—	696,892	—	696,892
State and municipal securities	1,620		181	—	—	—	1,801
Other investments	—		—	15,145	1,851	3,108	20,104
Total fair value	$	21,484	71,760	620,318	3,066,272	3,108	3,782,942

Schedule of Activity for Available-for-Sale Securities

Proceeds from sales, gross gains, and gross losses on sales of securities available for sale for the three months ended March 31, 2017 and 2016 are presented below. The specific identification method is used to reclassify gains and losses out of other comprehensive income at the time of sale.

	Three Months Ended March 31,
(in thousands)	2017			2016
Proceeds from sales of investment securities available for sale	$	282,629		243,609
Gross realized gains on sales	7,702			954
Gross realized losses on sales	(34		)	(887	)
Investment securities gains, net	$	7,668		67