Loans and Allowance for Credit Losses Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Receivables [Abstract]
Allowance for loan losses	$ 167,485	$ 177,701	$ 184,144	$ 191,685	$ 197,089	$ 202,780
Reserve for unfunded lending commitments	1,968		1,787
Allowance for credit losses	$ 169,453	$ 179,658	$ 185,931	$ 193,442	$ 199,006	$ 204,917