Fair Value Part 1 (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$ 2,382,441	$ 2,194,154
Loans held for sale	120,446	149,169
Mortgage servicing rights	67,614	67,834	51,529	47,341
Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	100	502
U.S. Government agency obligations	163,969	169,472
Obligations of states and political subdivisions	172,437	171,738
Mortgage-backed securities	2,008,891	1,788,505
Asset-backed securities and structure financial products	37,044	63,937
Securities available for sale	2,382,441	2,194,154
Loans held for sale	120,446	149,169
Mortgage servicing rights	67,614	67,834
Other assets - derivatives	5,960	4,994
Other liabilities - derivatives	4,485	3,298
Level 1 [Member] | Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	0	0
U.S. Government agency obligations	0	0
Obligations of states and political subdivisions	0	0
Mortgage-backed securities	0	0
Asset-backed securities and structure financial products	0	0
Securities available for sale	0	0
Loans held for sale	0	0
Mortgage servicing rights	0	0
Other assets - derivatives	(630)	(2,579)
Other liabilities - derivatives	630	581
Level 2 [Member] | Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	100	502
U.S. Government agency obligations	163,969	169,472
Obligations of states and political subdivisions	172,437	171,738
Mortgage-backed securities	2,008,891	1,788,505
Asset-backed securities and structure financial products	37,044	63,937
Securities available for sale	2,382,441	2,194,154
Loans held for sale	120,446	149,169
Mortgage servicing rights	0	0
Other assets - derivatives	5,774	7,447
Other liabilities - derivatives	3,855	2,717
Level 3 [Member] | Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities	0	0
U.S. Government agency obligations	0	0
Obligations of states and political subdivisions	0	0
Mortgage-backed securities	0	0
Asset-backed securities and structure financial products	0	0
Securities available for sale	0	0
Loans held for sale	0	0
Mortgage servicing rights	67,614	67,834
Other assets - derivatives	816	126
Other liabilities - derivatives	$ 0	$ 0