Fair Value Measurement (Assets and Liabilities Measured at Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets:
Equity securities, trading, at fair value	$ 322,353	$ 314,482
Other investments	79,133	86,057
Other investments
Total assets at fair value	3,395,111	3,752,976
Level 3 [Member] \| State and municipal bonds [Member]
Other investments
Total assets at fair value	0	5,000
Level 3 [Member] \| Corporate debt, limited observable inputs [Member]
Other investments
Total assets at fair value	14,500	13,100
Level 3 [Member] \| Other asset-backed securities [Member]
Other investments
Total assets at fair value	800	4,800
Fair Value, Measurements, Recurring [Member]
Assets:
Other investments	30,611	28,958
Other investments
Total assets at fair value	3,232,487	3,619,726
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury obligations [Member]
Assets:
Fixed maturities, available for sale	123,892	166,512
Fair Value, Measurements, Recurring [Member] \| U.S. Government-sponsored enterprise obligations [Member]
Assets:
Fixed maturities, available for sale	26,334	39,563
Fair Value, Measurements, Recurring [Member] \| State and municipal bonds [Member]
Assets:
Fixed maturities, available for sale	940,635	1,062,615
Fair Value, Measurements, Recurring [Member] \| Corporate debt, multiple observable inputs [Member]
Assets:
Fixed maturities, available for sale	1,277,186	1,404,020
Fair Value, Measurements, Recurring [Member] \| Corporate debt, limited observable inputs [Member]
Assets:
Fixed maturities, available for sale	14,500	13,081
Fair Value, Measurements, Recurring [Member] \| Residential mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	238,387	276,056
Fair Value, Measurements, Recurring [Member] \| Agency commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	10,999	15,493
Fair Value, Measurements, Recurring [Member] \| Other commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	30,134	51,063
Fair Value, Measurements, Recurring [Member] \| Other asset-backed securities [Member]
Assets:
Fixed maturities, available for sale	98,220	116,624
Fair Value, Measurements, Recurring [Member] \| Financial [Member]
Assets:
Equity securities, trading, at fair value	67,764	79,341
Fair Value, Measurements, Recurring [Member] \| Utilities/Energy [Member]
Assets:
Equity securities, trading, at fair value	41,050	25,629
Fair Value, Measurements, Recurring [Member] \| Consumer oriented [Member]
Assets:
Equity securities, trading, at fair value	56,470	65,670
Fair Value, Measurements, Recurring [Member] \| Industrial [Member]
Assets:
Equity securities, trading, at fair value	48,305	55,460
Fair Value, Measurements, Recurring [Member] \| Fixed Income Funds [Member]
Assets:
Equity securities, trading, at fair value	76,316	55,196
Fair Value, Measurements, Recurring [Member] \| All other [Member]
Assets:
Equity securities, trading, at fair value	32,448	33,186
Fair Value, Measurements, Recurring [Member] \| Short-term Investments [Member]
Assets:
Short-term investments	119,236	131,259
Fair Value, Measurements, Recurring [Member] \| Accounting Standards Update 2015-07 [Member]
Other investments
LP/LLC interests carried at NAV which approximates fair value. These interests, reported as a part of Investment in unconsolidated subsidiaries, are not categorized within the fair value hierarchy.	162,624	133,250
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Assets:
Other investments	3,478	6,050
Other investments
Total assets at fair value	400,255	451,731
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| U.S. Treasury obligations [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| U.S. Government-sponsored enterprise obligations [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| State and municipal bonds [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Corporate debt, multiple observable inputs [Member]
Assets:
Fixed maturities, available for sale	2,362	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Corporate debt, limited observable inputs [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Residential mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Agency commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Other commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Other asset-backed securities [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Financial [Member]
Assets:
Equity securities, trading, at fair value	67,764	79,341
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Utilities/Energy [Member]
Assets:
Equity securities, trading, at fair value	41,050	25,629
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Consumer oriented [Member]
Assets:
Equity securities, trading, at fair value	56,470	65,670
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Industrial [Member]
Assets:
Equity securities, trading, at fair value	48,305	55,460
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Fixed Income Funds [Member]
Assets:
Equity securities, trading, at fair value	76,316	55,196
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| All other [Member]
Assets:
Equity securities, trading, at fair value	18,239	33,186
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| Short-term Investments [Member]
Assets:
Short-term investments	86,271	131,199
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Assets:
Other investments	27,133	22,908
Other investments
Total assets at fair value	2,816,975	3,145,120
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| U.S. Treasury obligations [Member]
Assets:
Fixed maturities, available for sale	123,892	166,512
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| U.S. Government-sponsored enterprise obligations [Member]
Assets:
Fixed maturities, available for sale	26,334	39,563
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| State and municipal bonds [Member]
Assets:
Fixed maturities, available for sale	940,635	1,057,590
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Corporate debt, multiple observable inputs [Member]
Assets:
Fixed maturities, available for sale	1,274,824	1,404,020
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Corporate debt, limited observable inputs [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Residential mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	238,387	276,056
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Agency commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	10,999	15,493
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Other commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	30,134	51,063
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Other asset-backed securities [Member]
Assets:
Fixed maturities, available for sale	97,463	111,855
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Financial [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Utilities/Energy [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Consumer oriented [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Industrial [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Fixed Income Funds [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| All other [Member]
Assets:
Equity securities, trading, at fair value	14,209	0
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Short-term Investments [Member]
Assets:
Short-term investments	32,965	60
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Assets:
Other investments	0	0
Other investments
Total assets at fair value	15,257	22,875
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| U.S. Treasury obligations [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| U.S. Government-sponsored enterprise obligations [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| State and municipal bonds [Member]
Assets:
Fixed maturities, available for sale	0	5,025
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Corporate debt, multiple observable inputs [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Corporate debt, limited observable inputs [Member]
Assets:
Fixed maturities, available for sale	14,500	13,081
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Residential mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Agency commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Other commercial mortgage-backed securities [Member]
Assets:
Fixed maturities, available for sale	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Other asset-backed securities [Member]
Assets:
Fixed maturities, available for sale	757	4,769
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Financial [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Utilities/Energy [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Consumer oriented [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Industrial [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Fixed Income Funds [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| All other [Member]
Assets:
Equity securities, trading, at fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member] \| Short-term Investments [Member]
Assets:
Short-term investments	$ 0	$ 0

Fair Value Measurement (Assets and Liabilities Measured at Fair Value) (Details) - USD ($)
$ in Thousands

Dec. 31, 2015

Dec. 31, 2014

Assets:

Equity securities, trading, at fair value

$ 322,353

$ 314,482

Other investments

79,133

86,057

Other investments

Total assets at fair value