Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014 Security	Jun. 30, 2013	Jun. 30, 2014 Security	Jun. 30, 2013	Mar. 31, 2014	Dec. 31, 2013 Security	Mar. 31, 2013	Dec. 31, 2012
Investment Securities [Line Items]
Held to Maturity, Amortized Cost	$ 1,826,143,000		$ 1,826,143,000			$ 1,731,737,000
Available for sale	783,205,000		783,205,000			829,692,000
Fair value of trading securities	14,221,000		14,221,000			14,264,000
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	80		80			133
Fair value of investments held to maturity pledged as collateral	925,900,000		925,900,000
Weighted-average remaining expected life of residential mortgage-backed securities held to maturity, years			8 years
Amortized Cost	795,545,000		795,545,000			866,904,000
Gross unrealized losses	21,279,000		21,279,000			46,262,000
Gross unrealized losses	21,279,000		21,279,000			46,262,000
Fair value of securities available for sale pledged as collateral	525,300,000		525,300,000
Weighted-average remaining expected life of residential mortgage-backed securities available for sale, years			5 years 2 months 5 days
Credit factors risk percentage			25.00%
Gains (losses) on securities transactions, net	7,000	41,000	(1,000)	3,999,000
Interest income on trading securities	291,000	413,000	581,000	855,000
Amortized Cost		941,000
Gross gains, Sales transactions	0	1,000	0	3,381,000
The credit loss component of cumulative other-than-temporary impairment losses recognized in earnings	9,682,000	33,102,000	9,682,000	33,102,000	9,792,000	9,990,000	33,177,000	33,290,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position	87		87			99
Trust Preferred Securities [Member] | Previously Other-Than-Temporarily Impaired Securities [Member]
Investment Securities [Line Items]
Available for sale	4,500,000		4,500,000
Amortized Cost	5,400,000		5,400,000
Trust Preferred Securities [Member] | Non-Rated [Member]
Investment Securities [Line Items]
Number of security positions in the securities held to maturity portfolio in an unrealized loss position	4		4
Pooled Trust Preferred Securities [Member]
Investment Securities [Line Items]
Available for sale	11,100,000		11,100,000
Amortized Cost	13,500,000		13,500,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position	3		3			3
Pooled Trust Preferred Securities [Member] | Investment Grade [Member]
Investment Securities [Line Items]
Gross unrealized losses	1,500,000		1,500,000
Number of security positions in the securities available for sale portfolio in an unrealized loss position	1		1
Pooled Trust Preferred Securities [Member] | Non-Investment Grade [Member]
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position	2		2
Perpetual Preferred Securities [Member]
Investment Securities [Line Items]
Number of security positions in the securities available for sale portfolio in an unrealized loss position	2		2
Three Private Label Mortgage-Backed Securities [Member]
Investment Securities [Line Items]
Available for sale	21,500,000		21,500,000
Number of investment grade private label mortgage-backed securities								5
Amortized Cost	21,800,000		21,800,000
Three Private Label Mortgage-Backed Securities [Member] | Investment Grade [Member]
Investment Securities [Line Items]
Gross unrealized losses	407,000		407,000
Three Private Label Mortgage-Backed Securities [Member] | Previously Other-Than-Temporarily Impaired Securities [Member]
Investment Securities [Line Items]
Number of investment grade private label mortgage-backed securities								3
Three Private Label Mortgage-Backed Securities [Member] | Previously Other-Than-Temporarily Impaired Securities [Member] | Investment Grade [Member]
Investment Securities [Line Items]
Number of investment grade private label mortgage-backed securities	4		4
Obligations of States and Political Subdivisions [Member]
Investment Securities [Line Items]
Held to Maturity, Amortized Cost	515,402,000		515,402,000			545,886,000
Available for sale	38,015,000		38,015,000			37,700,000
Amortized Cost	38,934,000		38,934,000			39,112,000
Gross unrealized losses	1,014,000		1,014,000			2,163,000
Gross unrealized losses	1,014,000		1,014,000			2,163,000
Obligations of States and Political Subdivisions [Member] | Other Than Temporarily Impaired Securities [Member]
Investment Securities [Line Items]
Available for sale	19,000,000		19,000,000
Amortized Cost	18,400,000		18,400,000
Gross unrealized losses	3,500,000		3,500,000
Investment carrying value	553,400,000		553,400,000
Investment carrying value percentage			53.00%
Residential Mortgage-Backed Securities [Member]
Investment Securities [Line Items]
Held to Maturity, Amortized Cost	1,019,086,000		1,019,086,000			886,043,000
Available for sale	478,132,000		478,132,000			508,029,000
Amortized Cost	481,781,000		481,781,000			524,781,000
Gross unrealized losses	7,888,000		7,888,000			20,719,000
Gross unrealized losses	7,888,000		7,888,000			20,719,000
The credit loss component of cumulative other-than-temporary impairment losses recognized in earnings	$ 0		$ 0