Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Investment Securities
Total investment securities available-for-sale, Amortized Cost	$ 819,918	$ 819,918		$ 849,139
Total investment securities available-for-sale, Gross Unrealized Gains	21,066	21,066		32,313
Total investment securities available-for-sale, Gross Unrealized Losses	(6,636)	(6,636)		(688)
Total investment securities available-for-sale, Fair Value	834,348	834,348		880,764
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Due in one year or less	128,276	128,276
Due after one year through five years	346,667	346,667
Due after five years through ten years	61,903	61,903
Due after ten years	650	650
Mortgage-backed securities	280,255	280,255
Total debt securities available-for-sale	817,751	817,751
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Due in one year or less	127,885	127,885
Due after one year through five years	352,734	352,734
Due after five years through ten years	61,568	61,568
Due after ten years	616	616
Mortgage-backed securities	284,360	284,360
Total debt securities available-for-sale	827,163	827,163
Other-than-temporary-impairment (OTTI) write-downs		0	0
Gross realized gains and losses
Gross realized gains	903	903	275
Gross realized losses	(931)	(931)
Net realized (losses) gains	(28)	(28)	275
U.S. Treasury and Federal agencies securities
Investment Securities
Total investment securities available-for-sale, Amortized Cost	394,063	394,063		410,983
Total investment securities available-for-sale, Gross Unrealized Gains	5,698	5,698		11,353
Total investment securities available-for-sale, Gross Unrealized Losses	(3,468)	(3,468)		(83)
Total investment securities available-for-sale, Fair Value	396,293	396,293		422,253
U.S. States and political subdivisions securities
Investment Securities
Total investment securities available-for-sale, Amortized Cost	111,843	111,843		100,055
Total investment securities available-for-sale, Gross Unrealized Gains	3,821	3,821		5,864
Total investment securities available-for-sale, Gross Unrealized Losses	(984)	(984)		(482)
Total investment securities available-for-sale, Fair Value	114,680	114,680		105,437
Mortgage-backed securities - Federal agencies
Investment Securities
Total investment securities available-for-sale, Amortized Cost	280,255	280,255		301,136
Total investment securities available-for-sale, Gross Unrealized Gains	6,277	6,277		11,296
Total investment securities available-for-sale, Gross Unrealized Losses	(2,172)	(2,172)		(25)
Total investment securities available-for-sale, Fair Value	284,360	284,360		312,407
Corporate debt securities
Investment Securities
Total investment securities available-for-sale, Amortized Cost	30,890	30,890		30,897
Total investment securities available-for-sale, Gross Unrealized Gains	242	242		445
Total investment securities available-for-sale, Gross Unrealized Losses	(9)	(9)		(94)
Total investment securities available-for-sale, Fair Value	31,123	31,123		31,248
Foreign government and other securities
Investment Securities
Total investment securities available-for-sale, Amortized Cost	700	700		3,700
Total investment securities available-for-sale, Gross Unrealized Gains	7	7		26
Total investment securities available-for-sale, Fair Value	707	707		3,726
Total debt securities
Investment Securities
Total investment securities available-for-sale, Amortized Cost	817,751	817,751		846,771
Total investment securities available-for-sale, Gross Unrealized Gains	16,045	16,045		28,984
Total investment securities available-for-sale, Gross Unrealized Losses	(6,633)	(6,633)		(684)
Total investment securities available-for-sale, Fair Value	827,163	827,163		875,071
Marketable equity securities
Investment Securities
Total investment securities available-for-sale, Amortized Cost	2,167	2,167		2,368
Total investment securities available-for-sale, Gross Unrealized Gains	5,021	5,021		3,329
Total investment securities available-for-sale, Gross Unrealized Losses	(3)	(3)		(4)
Total investment securities available-for-sale, Fair Value	$ 7,185	$ 7,185		$ 5,693