Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 19,281	$ 27,640	$ 37,447	$ 45,649
Other comprehensive (loss) income, net of tax:
Unrealized net holding (losses) gains arising during the period (pre-tax amounts of ($5,277), $8,267, ($434) and $16,892)	(3,223)	4,992	(266)	10,200
Reclassification adjustment for net gains related to securities available for sale included in net income (pre-tax amounts of $26, $14, $40 and $21)	(16)	(8)	(24)	(13)
Amortization of unrealized net gains and losses related to the reclassification of available for sale investment securities to held to maturity (pre-tax amounts of $307, $-, $614 and $-)	205	0	410	0
Pension and other benefits:
Amortization of prior service cost and actuarial gains (pre-tax amounts of $560, $19, $1,120 and $38)	342	11	684	23
Total other comprehensive (loss) income	(2,692)	4,995	804	10,210
Comprehensive income	$ 16,589	$ 32,635	$ 38,251	$ 55,859