CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 18,673	$ 15,344	$ 55,243	$ 46,401
Other comprehensive (loss) income, net of tax
Unrealized gains (losses) on investment securities arising during the period	3,057	(256)	4,287	10,077
Change in retirement obligation	220	189	624	663
Unrealized gain (loss) on derivatives	128	760	(771)	(334)
Unrealized gain (loss) on foreign currency exchange	91	(12)	50	(13)
Other comprehensive income (loss)	3,496	681	4,190	10,393
Comprehensive income	$ 22,169	$ 16,025	$ 59,433	$ 56,794