Amortized Cost and Fair Value of AFS Investment Securities (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Total Investment Securities, Weighted Yield	3.10%	2.71%
Total Investment Securities, Amortized Cost	$ 3,208,941,000	$ 3,587,677,000
Total Investment Securities, Gross Unrealized Gains	49,801,000	101,778,000
Total Investment Securities, Gross Unrealized Losses	(35,913,000)	(6,450,000)
Total Investment Securities, Fair Value	3,222,829,000	3,683,005,000
U.S. government and federal agency
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing within One Year, Weighted Yield		1.62%
Maturing within One Year, Amortized Cost		201,000
Maturing within One Year, Gross Unrealized Gains		1,000
Maturing within One Year, Gross Unrealized Losses		0
Maturing within One Year, Fair Value		202,000
U.S. government sponsored enterprises
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing after One Through Five Year, Weighted Yield	2.32%	2.30%
Maturing after Five Through Ten Years, Weighted Yield	2.00%	2.03%
Total Investment Securities, Weighted Yield	2.32%	2.29%
Maturing after One Through Five Years, Amortized Cost	10,405,000	17,064,000
Maturing after Five Through Ten Years, Amortized Cost	36,000	44,000
Total Investment Securities, Amortized Cost	10,441,000	17,108,000
Maturing after One Through Five Years Gross Unrealized Gains	187,000	371,000
Maturing after Five Through Ten Years Gross Unrealized Gains	0	1,000
Total Investment Securities, Gross Unrealized Gains	187,000	372,000
Maturing after One Through Five Years, Gross Unrealized Losses	0	0
Maturing after Five Through Ten Years, Gross Unrealized Losses	0	0
Total Investment Securities, Gross Unrealized Losses	0	0
Maturing after One Through Five Years, Fair Value	10,592,000	17,435,000
Maturing after Five Through Ten Years, Fair Value	36,000	45,000
Total Investment Securities, Fair Value	10,628,000	17,480,000
State and local governments
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing within One Year, Weighted Yield	2.22%	2.01%
Maturing after One Through Five Year, Weighted Yield	2.06%	2.11%
Maturing after Five Through Ten Years, Weighted Yield	3.21%	2.95%
Maturing after Ten Years, Weighted Yield	4.41%	4.70%
Total Investment Securities, Weighted Yield	4.06%	4.29%
Maturing within One Year, Amortized Cost	5,964,000	4,288,000
Maturing after One Through Five Years, Amortized Cost	174,826,000	149,497,000
Maturing after Five Through Ten Years, Amortized Cost	58,835,000	38,346,000
Maturing after Ten Years, Amortized Cost	1,137,722,000	935,897,000
Total Investment Securities, Amortized Cost	1,377,347,000	1,128,028,000
Maturing within One Year, Gross Unrealized Gains	57,000	28,000
Maturing after One Through Five Years Gross Unrealized Gains	3,486,000	4,142,000
Maturing after Five Through Ten Years Gross Unrealized Gains	831,000	1,102,000
Maturing after Ten Years, Gross Unrealized Gains	27,247,000	82,823,000
Total Investment Securities, Gross Unrealized Gains	31,621,000	88,095,000
Maturing within One Year, Gross Unrealized Losses	0	(2,000)
Maturing after One Through Five Years, Gross Unrealized Losses	(448,000)	(142,000)
Maturing after Five Through Ten Years, Gross Unrealized Losses	(1,040,000)	(99,000)
Maturing after Ten Years, Gross Unrealized Losses	(22,402,000)	(1,362,000)
Total Investment Securities, Gross Unrealized Losses	(23,890,000)	(1,605,000)
Maturing within One Year, Fair Value	6,021,000	4,314,000
Maturing after One Through Five Years, Fair Value	177,864,000	153,497,000
Maturing after Five Through Ten Years, Fair Value	58,626,000	39,349,000
Maturing after Ten Years, Fair Value	1,142,567,000	1,017,358,000
Total Investment Securities, Fair Value	1,385,078,000	1,214,518,000
Corporate bonds
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing within One Year, Weighted Yield	2.17%	1.73%
Maturing after One Through Five Year, Weighted Yield	2.09%	2.22%
Maturing after Five Through Ten Years, Weighted Yield	2.23%	2.23%
Total Investment Securities, Weighted Yield	2.11%	2.19%
Maturing within One Year, Amortized Cost	91,687,000	18,412,000
Maturing after One Through Five Years, Amortized Cost	341,799,000	250,027,000
Maturing after Five Through Ten Years, Amortized Cost	6,851,000	16,144,000
Total Investment Securities, Amortized Cost	440,337,000	284,583,000
Maturing within One Year, Gross Unrealized Gains	719,000	51,000
Maturing after One Through Five Years Gross Unrealized Gains	3,203,000	4,018,000
Maturing after Five Through Ten Years Gross Unrealized Gains	0	381,000
Total Investment Securities, Gross Unrealized Gains	3,922,000	4,450,000
Maturing within One Year, Gross Unrealized Losses	0	0
Maturing after One Through Five Years, Gross Unrealized Losses	(1,676,000)	(238,000)
Maturing after Five Through Ten Years, Gross Unrealized Losses	(82,000)	0
Total Investment Securities, Gross Unrealized Losses	(1,758,000)	(238,000)
Maturing within One Year, Fair Value	92,406,000	18,463,000
Maturing after One Through Five Years, Fair Value	343,326,000	253,807,000
Maturing after Five Through Ten Years, Fair Value	6,769,000	16,525,000
Total Investment Securities, Fair Value	442,501,000	288,795,000
Collateralized debt obligations
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Maturing after Ten Years, Weighted Yield		8.03%
Maturing after Ten Years, Amortized Cost		1,708,000
Maturing after Ten Years, Gross Unrealized Gains		0
Maturing after Ten Years, Gross Unrealized Losses		0
Maturing after Ten Years, Fair Value		1,708,000
Residential mortgage-backed securities
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale
Total Investment Securities, Weighted Yield	2.48%	1.95%
Total Investment Securities, Amortized Cost	1,380,816,000	2,156,049,000
Total Investment Securities, Gross Unrealized Gains	14,071,000	8,860,000
Total Investment Securities, Gross Unrealized Losses	(10,265,000)	(4,607,000)
Total Investment Securities, Fair Value	$ 1,384,622,000	$ 2,160,302,000