Securities (Additional Information) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Investments [Line Items]
Unrealized gains on securities available-for-sale included in accumulated other comprehensive income, net of deferred taxes	$ 12,943	$ 11,128
Unrealized gains on securities available-for-sale included in accumulated other comprehensive income, deferred taxes	7,000	6,000
Investment securities with unrealized losses that are considered temporary	124,054	62,776
Number of investment securities which had unrealized losses for twelve months or longer	17	20
Investment securities with unrealized losses for twelve months or longer	8,174	14,787
Loss on investments	2,498	2,076	(409)
Other than temporary impairment losses	39
Security pledged as collateral, amortized cost	465,000	435,800
Security pledged as collateral, fair value	482,400	454,200
Carrying value of investments sold	113,000
Private issue collateralized mortgage obligations [Member]
Schedule of Investments [Line Items]
Investment securities with unrealized losses that are considered temporary	8,174	10,641
Investment securities with unrealized losses for twelve months or longer	8,174	10,641
Other than temporary impairment losses	176,000
Proceeds from sale of investments		7,800
Private issue collateralized mortgage obligations [Member] | Noninvestment grade [Member]
Schedule of Investments [Line Items]
Investment securities with unrealized losses that are considered temporary	7,500	9,700
Agency Securities [Member]
Schedule of Investments [Line Items]
Proceeds from sale of investments		10,200
Mortgage-backed securities [Member]
Schedule of Investments [Line Items]
Investment securities with unrealized losses that are considered temporary	42,782
Investment securities with unrealized losses for twelve months or longer
Municipal bonds [Member]
Schedule of Investments [Line Items]
Proceeds from sale of investments		7,300
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Investment securities with unrealized losses that are considered temporary	73,098	37,994
Investment securities with unrealized losses for twelve months or longer
Pass Through Securities [Member]
Schedule of Investments [Line Items]
Proceeds from sale of investments		$ 29,300