Investments (Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Investment securities available for sale:
Less than 12 months, fair value	$ 3,215,181	$ 664,243	$ 1,639,404
12 months or more, fair value	31,766	9,433	1,678
Total fair value	3,246,947	673,676	1,641,082
Less than 12 months, unrealized losses	32,570	581	1,529
12 months or more, unrealized losses	851	127	37
Total unrealized losses	33,421	708	1,566
U. S. Treasury
Investment securities available for sale:
Less than 12 months, fair value	76,846	120,045	528,579
12 months or more, fair value	0	0	0
Total fair value	76,846	120,045	528,579
Less than 12 months, unrealized losses	207	12	156
12 months or more, unrealized losses	0	0	0
Total unrealized losses	207	12	156
Government Agency
Investment securities available for sale:
Less than 12 months, fair value	1,656,424	407,498	818,772
12 months or more, fair value	0	0	0
Total fair value	1,656,424	407,498	818,772
Less than 12 months, unrealized losses	5,379	337	565
12 months or more, unrealized losses	0	0	0
Total unrealized losses	5,379	337	565
Mortgage Backed Securities, Other [Member]
Investment securities available for sale:
Less than 12 months, fair value	1,481,083	135,880	292,053
12 months or more, fair value	31,766	9,433	1,668
Total fair value	1,512,849	145,313	293,721
Less than 12 months, unrealized losses	26,961	214	808
12 months or more, unrealized losses	851	127	37
Total unrealized losses	27,812	341	845
Investment securities held to maturity:
Less than 12 months, fair value	0	0	0
Less than 12 months, unrealized losses	0	0	0
12 months or more, fair value	15	17	19
12 months or more, unrealized losses	27	27	27
Total fair value	15	17	19
Total unrealized losses	27	27	27
Other Debt Obligations
Investment securities available for sale:
Less than 12 months, fair value	828	820
12 months or more, fair value	0	0
Total fair value	828	820
Less than 12 months, unrealized losses	23	18
12 months or more, unrealized losses	0	0
Total unrealized losses	23	18
State, County and Municipal
Investment securities available for sale:
Less than 12 months, fair value			0
12 months or more, fair value			10
Total fair value			10
Less than 12 months, unrealized losses			0
12 months or more, unrealized losses			0
Total unrealized losses			$ 0