Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Comprehensive Income [Abstract]
Net income	$ 17,507	$ 13,926	$ 7,004
Other comprehensive income (loss), net of tax:
Reclassification adjustment of OTTI losses included in income	870	342	5,576
Reclassification adjustment of OTTI losses included in income, Tax effect	(265)	(119)	(1,121)
Unrealized gains and losses on securities available-for-sale: Reclassification adjustment on OTTI losses included in income	605	223	4,455
Unrealized holding gains on available-for-sale securities	19,819	8,990	3,822
Unrealized holding gains on available-for-sale securities, Tax effect	(7,444)	(3,486)	(1,791)
Unrealized gains and losses on securities available-for-sale: Unrealized holding gains arising during the period	12,375	5,504	2,031
Reclassification adjustment for realized gains arising during this period	(2,882)	(3,976)	(4,237)
Reclassification adjustment for realized gains arising during this period, Tax effect	879	1,380	852
Unrealized gains and losses on securities available-for-sale: Reclassification adjustment for realized gains arising during the period	(2,003)	(2,596)	(3,385)
Unrealized holding gains on securities transferred from available-for-sale to held-to-maturity securities	0	291	0
Unrealized holding gains on securities transferred from available-for-sale to held-to-maturity securities, Tax effect	0	(110)	0
Unrealized gains and losses on securities available-for-sale: Unrealized holding losses / gains on securities transferred from available-for-sale to held-to-maturity securities	0	181	0
Unrealized holding gains on securities transferred from available-for-sale to held-to-maturity securities	(2)	(46)	0
Unrealized holding gains on securities transferred from available-for-sale to held-to-maturity securities, Tax effect	1	28	0
Unrealized gains and losses on securities available-for-sale: Amortization of unrealized holding gains on securities transferred from available-for-sale to held-to-maturity securities	(1)	(18)	0
Unrealized gains and losses on securities available-for-sale: Net unrealized gains (losses) on investment securities	10,976	3,294	3,101
Pension plan:
Actuarial loss	(790)	(1,649)	0
Acturial loss, Tax effect	323	584	0
Actuarial loss	(467)	(1,065)
Total other comprehensive income	10,509	2,229	3,101
Total comprehensive income	$ 28,016	$ 16,155	$ 10,105