Derivative and Hedging Activities - Schedule of Notional Amounts and Gross Fair Values of Derivative Assets and Derivative Liabilities (Detail) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Notional amount	$ 3,562,865,000	$ 2,893,041,000
Fair value, asset	108,149,000	53,202,000
Liability	100,817,000	51,605,000
Credit Risk Contracts [Member]
Derivatives, Fair Value [Line Items]
Fair value, asset	47,000	7,000
Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Notional amount	1,921,446,000	1,514,144,000
Fair value, asset	10,081,000	3,197,000
Liability	100,351,000	51,453,000
Subject to Master Netting Arrangement [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional amount	450,000,000	250,000,000
Fair value, asset	10,022,000	3,178,000
Liability	1,669,000	962,000
Subject to Master Netting Arrangement [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Notional amount	1,470,266,000	1,262,964,000
Fair value, asset		1,000
Liability	98,682,000	50,491,000
Subject to Master Netting Arrangement [Member] \| Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional amount	1,180,000	1,180,000
Fair value, asset	59,000	18,000
Not Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Notional amount	1,641,419,000	1,378,897,000
Fair value, asset	98,068,000	50,005,000
Liability	466,000	152,000
Not Subject to Master Netting Arrangement [Member] \| Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Notional amount	1,470,266,000	1,262,964,000
Fair value, asset	98,021,000	49,998,000
Liability		1,000
Not Subject to Master Netting Arrangement [Member] \| Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional amount	1,180,000	1,180,000
Liability	59,000	18,000
Not Subject to Master Netting Arrangement [Member] \| Credit Risk Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional amount	169,973,000	114,753,000
Fair value, asset	47,000	7,000
Liability	$ 407,000	$ 133,000

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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