Fair Value Part 1 (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total, Securities Available for Sale, Estimated Fair Value	$ 3,511,683	$ 2,657,745
Loans held for sale	202,699	257,986
Mortgage servicing rights	60,380	47,341	43,580	43,274
Other assets - derivatives	6,342	5,241
Other liabilities - derivatives	3,560	5,329
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	505
U.S. Government agency obligations	272,857	105,745
Obligations of states and political subdivisions	212,204	215,761
Mortgage-backed securities	2,792,152	2,094,612
Asset-backed securities	233,965	241,627
Total, Securities Available for Sale, Estimated Fair Value	3,511,683	2,657,745
Loans held for sale	202,699	257,986
Mortgage servicing rights	60,380	47,341
Other assets - derivatives	4,615	7,107
Other liabilities - derivatives	(5,936)	6,612
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	0
U.S. Government agency obligations	0	0
Obligations of states and political subdivisions	0	0
Mortgage-backed securities	0	0
Asset-backed securities	0	0
Total, Securities Available for Sale, Estimated Fair Value	0	0
Loans held for sale	0	0
Mortgage servicing rights	0	0
Other assets - derivatives	(2,099)	(440)
Other liabilities - derivatives	633	545
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	505
U.S. Government agency obligations	272,857	105,745
Obligations of states and political subdivisions	212,204	215,761
Mortgage-backed securities	2,792,152	2,094,612
Asset-backed securities	233,965	241,627
Total, Securities Available for Sale, Estimated Fair Value	3,511,683	2,657,745
Loans held for sale	202,699	257,986
Mortgage servicing rights	0	0
Other assets - derivatives	6,367	5,263
Other liabilities - derivatives	(6,569)	6,067
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	0
U.S. Government agency obligations	0	0
Obligations of states and political subdivisions	0	0
Mortgage-backed securities	0	0
Asset-backed securities	0	0
Total, Securities Available for Sale, Estimated Fair Value	0	0
Loans held for sale	0	0
Mortgage servicing rights	60,380	47,341
Other assets - derivatives	347	2,284
Other liabilities - derivatives	$ 0	$ 0