CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 15,344	$ 14,911	$ 46,401	$ 44,564
Other comprehensive (loss) income, net of tax
Unrealized gains (losses) on investment securities arising during the period	(256)	(4,003)	10,077	(22,570)
Change in retirement obligation	189	1,166	663	11,976
Unrealized gain (loss) on derivatives	760	(818)	(334)	(2)
Unrealized gain (loss) on foreign currency exchange	(12)	6	(13)	(21)
Other comprehensive income (loss)	681	(3,649)	10,393	(10,617)
Comprehensive income	$ 16,025	$ 11,262	$ 56,794	$ 33,947