Fair Value Part 1 (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$ 2,381,459	$ 2,374,567
Loans held for sale	150,365	132,196
Mortgage servicing rights	62,903	64,358	67,614	67,834
Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities		100
U.S. Government agency obligations	111,191	112,474
Obligations of states and political subdivisions	160,154	162,258
Mortgage-backed securities	2,080,016	2,068,035
Asset-backed securities and structured financial products	30,098	31,700
Securities available for sale	2,381,459	2,374,567
Loans held for sale	150,365	132,196
Mortgage servicing rights	62,903	64,358
Other assets - derivatives	7,814	5,527
Other liabilities - derivatives	6,326	4,338
Level 1 [Member] | Recurring Basis [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 and structured financial products	0	0
Securities available for sale	0	0
Loans held for sale	0	0
Mortgage servicing rights	0	0
Other assets - derivatives	1,908	1,181
Other liabilities - derivatives	917	490
Level 2 [Member] | Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasury securities		100
U.S. Government agency obligations	111,191	112,474
Obligations of states and political subdivisions	160,154	162,258
Mortgage-backed securities	2,080,016	2,068,035
Asset-backed securities and structured financial products	30,098	31,700
Securities available for sale	2,381,459	2,374,567
Loans held for sale	150,365	132,196
Mortgage servicing rights	0	0
Other assets - derivatives	3,318	3,047
Other liabilities - derivatives	5,409	3,848
Level 3 [Member] | Recurring Basis [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 and structured financial products	0	0
Securities available for sale	0	0
Loans held for sale	0	0
Mortgage servicing rights	62,903	64,358
Other assets - derivatives	2,588	1,299
Other liabilities - derivatives	$ 0	$ 0