Securities - Amortized Cost and Fair Value of Held to Maturity Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	$ 2,370,388	$ 2,166,289
Securities Held to Maturity, Gross Unrealized Gains	21,304	32,903
Securities Held to Maturity, Gross Unrealized Losses	15,841	12,852
Securities Held to Maturity, Fair Value	2,375,851	2,186,340
U.S. Treasury and Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	50,000
Securities Held to Maturity, Gross Unrealized Losses	410
Securities Held to Maturity, Fair Value	49,590
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	185,890	180,615
Securities Held to Maturity, Gross Unrealized Gains	3,475	3,416
Securities Held to Maturity, Gross Unrealized Losses	1,166	1,144
Securities Held to Maturity, Fair Value	188,199	182,887
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	1,014,135	899,923
Securities Held to Maturity, Gross Unrealized Gains	15,585	23,897
Securities Held to Maturity, Gross Unrealized Losses	1,589	162
Securities Held to Maturity, Fair Value	1,028,131	923,658
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	1,120,363	1,085,751
Securities Held to Maturity, Gross Unrealized Gains	2,244	5,590
Securities Held to Maturity, Gross Unrealized Losses	12,676	11,546
Securities Held to Maturity, Fair Value	$ 1,109,931	$ 1,079,795

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.6)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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