Fair Value - by Balance Sheet Grouping (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Change During Period, Fair Value Disclosure [Member]	Jun. 30, 2012 Change During Period, Fair Value Disclosure [Member]	Jun. 30, 2013 MBS	Dec. 31, 2012 MBS	Jun. 30, 2013 Municipal Bonds	Dec. 31, 2012 Municipal Bonds	Jun. 30, 2013 Fair Value, Measurements, Nonrecurring [Member] Loans [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Loans [Member] Carrying Amount [Member]	Jun. 30, 2013 Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member] Carrying Amount [Member]	Jun. 30, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member]	Jun. 30, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] MBS	Jun. 30, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Jun. 30, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Carrying Amount [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] MBS	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 1 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Carrying Amount [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] MBS	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Carrying Amount [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Carrying Amount [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] MBS	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] MBS	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Municipal Bonds	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] Other [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Loans [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member] Mortgage Servicing Rights [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents																					$ 325,710,000	$ 331,550,000	$ 325,710,000	$ 331,550,000
Available for sale	1,538,880,000	1,513,157,000			1,343,181,000	1,308,838,000	195,530,000	204,306,000					1,538,880,000	1,513,157,000	1,343,181,000	1,308,838,000	195,530,000	204,306,000	169,000	13,000					0	0	0	0	0	0	0	0					1,538,880,000	1,513,157,000	1,538,880,000	1,513,157,000	1,538,880,000	1,513,157,000	1,343,181,000	1,308,838,000	195,530,000	204,306,000	169,000	13,000									0	0	0	0	0	0	0	0
Held to maturity																																					185,000	206,000	185,000	206,000
Loans held for sale			(24,572,000)	11,000									307,511,000	465,983,000											0	0											307,511,000	465,983,000	307,511,000	465,983,000	307,511,000	465,983,000															0	0
Loans receivable, net	36,338,000	23,177,000							66,620,000	172,172,000			36,338,000	23,177,000											0	0							0	0							0	0							0	0			6,868,866,000	6,101,749,000	6,930,174,000	6,154,296,000	36,338,000	23,177,000							66,620,000	172,172,000
Mortgage servicing rights, net	52,430,000	32,420,000																																																			52,430,000	32,420,000
Mortgage servicing rights, at fair value											52,430,000	32,420,000																							0	0															0	0			60,650,000	32,420,000											52,430,000	32,420,000
Other assets													19,503,000	11,183,000											0	0											115,596,000	108,642,000	115,596,000	108,642,000	19,503,000	11,183,000															0	0
Non-maturity deposits																																					4,879,525,000	4,697,147,000	4,879,525,000	4,697,147,000
Deposits with stated maturities																																					1,748,934,000	1,738,970,000	1,769,442,000	1,768,818,000
Borrowings																																					1,971,079,000	1,437,491,000	1,971,522,000	1,457,911,000
Other liabilities																																					1,088,000	4,025,000	1,088,000	4,025,000
FHLB stock	$ 96,100,000	$ 97,500,000