Borrowed Funds - Additional Information (Detail) - USD ($)		1 Months Ended			3 Months Ended								12 Months Ended
	Sep. 27, 2013	Aug. 31, 2016	Jul. 31, 2015	Jun. 30, 2015	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 01, 2016	Aug. 05, 2016	May 31, 2016
Debt Instrument [Line Items]
Weighted average interest rate for short-term borrowings					0.65%				0.69%				0.65%	0.69%
Prepaid long-term FHLB advances									$ 625,000,000					$ 625,000,000			$ 355,000,000	$ 87,000,000
Prepaid long-term FHLB stock									220,000,000					220,000,000			$ 50,000,000
Contractual amounts due in year two									795,000,000					795,000,000
Contractual amounts due in year three									50,000,000					50,000,000
Loss on extinguishment of debt					$ 0	$ 0	$ 315,000	$ 0	$ 51,129,000	$ 0	$ 0	$ 0	$ 315,000	$ 51,129,000	$ 10,132,000
Callable FHLB advances with scheduled maturities beyond 2017					10,000,000								10,000,000
Callable FHLB advances interest rates		3.69%							3.72%					3.72%		2.51%
FHLB advances		$ 405,000,000
Prepayment penalties paid to FHLB													20,000,000
Net carrying value of subordinated debentures					136,700,000				$ 130,600,000				136,700,000	$ 130,600,000
Fair value of securities					$ 1,500,000,000				$ 1,400,000,000				$ 1,500,000,000	$ 1,400,000,000
Interest rate swaps
Debt Instrument [Line Items]
Notional amount of terminated derivative		$ 125,000,000
Minimum
Debt Instrument [Line Items]
Callable FHLB advances interest rates					2.27%								2.27%
Maximum
Debt Instrument [Line Items]
Callable FHLB advances interest rates					3.25%								3.25%
Subordinated debentures
Debt Instrument [Line Items]
Subordinated notes, interest rate			5.00%
Debt matured and repaid			$ 100,000,000
Securities sold under agreements to repurchase
Debt Instrument [Line Items]
Weighted average interest rate for long-term borrowings					2.41%				3.35%				2.41%	3.35%
Subordinated notes
Debt Instrument [Line Items]
Subordinated notes				$ 100,000,000							$ 100,000,000
Subordinated notes, interest rate				4.55%
FHLB
Debt Instrument [Line Items]
Weighted average interest rate for long-term borrowings					3.37%				3.96%				3.37%	3.96%
Collateralized letter of credit					$ 100,000,000								$ 100,000,000
Long-term borrowings
Debt Instrument [Line Items]
Subordinated notes					$ 236,731,000				$ 230,573,000				$ 236,731,000	$ 230,573,000
Subordinated debentures
Debt Instrument [Line Items]
Subordinated notes	$ 125,000,000
Subordinated notes, interest rate	5.125%
Subordinated notes due September 2023 | Subordinated debentures
Debt Instrument [Line Items]
Effective interest rate					3.32%								3.32%