Investments (Amortized Cost and Estimated Fair Values of Investments Available-for-sale) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 680,725	$ 750,690
Gross Unrealized Gains	19,728	16,252
Gross Unrealized Losses	(8,346)	(15,658)
Estimated Fair Value	692,107	751,284
Available-for-Sale Securities [Member] | Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	723	723
Estimated Fair Value	723	723
Available-for-Sale Securities [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	680,002	749,967
Gross Unrealized Gains	19,728	16,252
Gross Unrealized Losses	(8,346)	(15,658)
Estimated Fair Value	691,384	750,561
Available-for-Sale Securities [Member] | Debt Securities [Member] | U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	144,473	147,688
Gross Unrealized Losses	(3,757)	(8,222)
Estimated Fair Value	140,716	139,466
Available-for-Sale Securities [Member] | Debt Securities [Member] | State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	157,854	159,524
Gross Unrealized Gains	9,731	6,060
Gross Unrealized Losses		(156)
Estimated Fair Value	167,585	165,428
Available-for-Sale Securities [Member] | Debt Securities [Member] | Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	374,326	439,054
Gross Unrealized Gains	9,995	10,188
Gross Unrealized Losses	(4,417)	(6,992)
Estimated Fair Value	379,904	442,250
Available-for-Sale Securities [Member] | Debt Securities [Member] | Corporate Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,000	2,000
Gross Unrealized Gains	2	4
Estimated Fair Value	2,002	2,004
Available-for-Sale Securities [Member] | Debt Securities [Member] | Trust Preferred [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,349	1,701
Gross Unrealized Losses	(172)	(288)
Estimated Fair Value	$ 1,177	$ 1,413