CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net income	$ 35,074	$ 29,724	$ 24,051
Securities available for sale:
Unrealized (losses) gains on securities arising during the period	(2,664)	1,622	1,099
Less: reclassification adjustment for net gains on securities realized in net income	768	415	311
Net unrealized (losses) gains on securities available for sale	(3,432)	1,207	788
Reclassification adjustment for change in non-credit portion of OTTI realized losses transferred to net income	124	88	111
Cash flow hedges:
Unrealized losses on cash flow hedges arising during the period	(333)	(942)	(915)
Less: reclassification adjustment for amount of gains on cash flow hedges realized in net income	454	486	252
Net unrealized gains (losses) on cash flow hedges	121	(456)	(663)
Defined benefit plan obligation adjustment	(5,417)	(6,759)	452
Total other comprehensive (loss) income, net of tax	(8,604)	(5,920)	688
Total comprehensive income	$ 26,470	$ 23,804	$ 24,739