Fair Value Measurement (Assets Measured at Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
AFS debt securities	$ 2,281,664	$ 2,288,785
Fixed maturities, trading	47,680	47,284
Equity investments	92,750	250,552
U.S. Treasury obligations
Assets:
AFS debt securities	129,260	110,467
U.S. Government-sponsored enterprise obligations
Assets:
AFS debt securities	12,410	17,340
State and municipal bonds
Assets:
AFS debt securities	291,667	296,093
Corporate debt, limited observable inputs | Level 3
Assets:
AFS debt securities	3,440	5,079
Residential mortgage-backed securities
Assets:
AFS debt securities	230,598	208,408
Agency commercial mortgage-backed securities
Assets:
AFS debt securities	13,363	8,221
Other commercial mortgage-backed securities
Assets:
AFS debt securities	79,124	71,868
Other asset-backed securities
Assets:
AFS debt securities	236,524	236,024
Other investments | Level 3
Assets:
Total assets categorized within the fair value hierarchy	1,338	3,086
Recurring
Assets:
Total assets categorized within the fair value hierarchy	3,081,612	3,233,830
Recurring | Level 1
Assets:
Fixed maturities, trading	0	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	406,617	545,607
Recurring | Level 2
Assets:
Fixed maturities, trading	47,680	47,284
Other assets	465	760
Total assets categorized within the fair value hierarchy	2,359,539	2,384,065
Recurring | Level 3
Assets:
Fixed maturities, trading	0	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	11,675	11,157
Recurring | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Fixed maturities, trading	47,680	47,284
Other assets	465	760
Total assets categorized within the fair value hierarchy	2,777,831	2,940,829
Recurring | U.S. Treasury obligations | Level 1
Assets:
AFS debt securities	0	0
Recurring | U.S. Treasury obligations | Level 2
Assets:
AFS debt securities	129,260	110,467
Recurring | U.S. Treasury obligations | Level 3
Assets:
AFS debt securities	0	0
Recurring | U.S. Treasury obligations | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	129,260	110,467
Recurring | U.S. Government-sponsored enterprise obligations | Level 1
Assets:
AFS debt securities	0	0
Recurring | U.S. Government-sponsored enterprise obligations | Level 2
Assets:
AFS debt securities	12,410	17,340
Recurring | U.S. Government-sponsored enterprise obligations | Level 3
Assets:
AFS debt securities	0	0
Recurring | U.S. Government-sponsored enterprise obligations | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	12,410	17,340
Recurring | State and municipal bonds | Level 1
Assets:
AFS debt securities	0	0
Recurring | State and municipal bonds | Level 2
Assets:
AFS debt securities	291,667	296,093
Recurring | State and municipal bonds | Level 3
Assets:
AFS debt securities	0	0
Recurring | State and municipal bonds | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	291,667	296,093
Recurring | Corporate debt, multiple observable inputs | Level 1
Assets:
AFS debt securities	0	0
Recurring | Corporate debt, multiple observable inputs | Level 2
Assets:
AFS debt securities	1,285,278	1,335,285
Recurring | Corporate debt, multiple observable inputs | Level 3
Assets:
AFS debt securities	0	0
Recurring | Corporate debt, multiple observable inputs | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	1,285,278	1,335,285
Recurring | Corporate debt, limited observable inputs | Level 1
Assets:
AFS debt securities	0	0
Recurring | Corporate debt, limited observable inputs | Level 2
Assets:
AFS debt securities	0	0
Recurring | Corporate debt, limited observable inputs | Level 3
Assets:
AFS debt securities	3,440	5,079
Recurring | Corporate debt, limited observable inputs | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	3,440	5,079
Recurring | Residential mortgage-backed securities | Level 1
Assets:
AFS debt securities	0	0
Recurring | Residential mortgage-backed securities | Level 2
Assets:
AFS debt securities	229,905	208,408
Recurring | Residential mortgage-backed securities | Level 3
Assets:
AFS debt securities	693	0
Recurring | Residential mortgage-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	230,598	208,408
Recurring | Agency commercial mortgage-backed securities | Level 1
Assets:
AFS debt securities	0	0
Recurring | Agency commercial mortgage-backed securities | Level 2
Assets:
AFS debt securities	13,363	8,221
Recurring | Agency commercial mortgage-backed securities | Level 3
Assets:
AFS debt securities	0	0
Recurring | Agency commercial mortgage-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	13,363	8,221
Recurring | Other commercial mortgage-backed securities | Level 1
Assets:
AFS debt securities	0	0
Recurring | Other commercial mortgage-backed securities | Level 2
Assets:
AFS debt securities	78,519	71,868
Recurring | Other commercial mortgage-backed securities | Level 3
Assets:
AFS debt securities	605	0
Recurring | Other commercial mortgage-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	79,124	71,868
Recurring | Other asset-backed securities | Level 1
Assets:
AFS debt securities	0	0
Recurring | Other asset-backed securities | Level 2
Assets:
AFS debt securities	230,925	233,032
Recurring | Other asset-backed securities | Level 3
Assets:
AFS debt securities	5,599	2,992
Recurring | Other asset-backed securities | Fair Value, Inputs, Level 1, 2 and 3
Assets:
AFS debt securities	236,524	236,024
Recurring | Financial | Level 1
Assets:
Equity investments	14,953	40,294
Recurring | Financial | Level 2
Assets:
Equity investments	0	0
Recurring | Financial | Level 3
Assets:
Equity investments	0	0
Recurring | Financial | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	14,953	40,294
Recurring | Utilities/Energy | Level 1
Assets:
Equity investments	447	21,195
Recurring | Utilities/Energy | Level 2
Assets:
Equity investments	0	0
Recurring | Utilities/Energy | Level 3
Assets:
Equity investments	0	0
Recurring | Utilities/Energy | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	447	21,195
Recurring | Consumer oriented | Level 1
Assets:
Equity investments	1,067	29,288
Recurring | Consumer oriented | Level 2
Assets:
Equity investments	0	0
Recurring | Consumer oriented | Level 3
Assets:
Equity investments	0	0
Recurring | Consumer oriented | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	1,067	29,288
Recurring | Industrial | Level 1
Assets:
Equity investments	1,286	26,440
Recurring | Industrial | Level 2
Assets:
Equity investments	0	0
Recurring | Industrial | Level 3
Assets:
Equity investments	0	0
Recurring | Industrial | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	1,286	26,440
Recurring | Bond funds | Level 1
Assets:
Equity investments	34,923	58,346
Recurring | Bond funds | Level 2
Assets:
Equity investments	0	0
Recurring | Bond funds | Level 3
Assets:
Equity investments	0	0
Recurring | Bond funds | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	34,923	58,346
Recurring | All other | Level 1
Assets:
Equity investments	17,135	52,512
Recurring | All other | Level 2
Assets:
Equity investments	0	0
Recurring | All other | Level 3
Assets:
Equity investments	0	0
Recurring | All other | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Equity investments	17,135	52,512
Recurring | Short-term investments | Level 1
Assets:
Short-term and other investments	336,426	317,313
Recurring | Short-term investments | Level 2
Assets:
Short-term and other investments	10,914	22,594
Recurring | Short-term investments | Level 3
Assets:
Short-term and other investments	0	0
Recurring | Short-term investments | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Short-term and other investments	347,340	339,907
Recurring | Other investments | Level 1
Assets:
Short-term and other investments	380	219
Recurring | Other investments | Level 2
Assets:
Short-term and other investments	29,153	32,713
Recurring | Other investments | Level 3
Assets:
Short-term and other investments	1,338	3,086
Recurring | Other investments | Fair Value, Inputs, Level 1, 2 and 3
Assets:
Short-term and other investments	30,871	36,018
Equities | Recurring | Equities | Fair Value Measured at Net Asset Value Per Share
Assets:
Total assets categorized within the fair value hierarchy	22,939	22,477
Equity investments | Recurring | Equities | Fair Value Measured at Net Asset Value Per Share
Assets:
Total assets categorized within the fair value hierarchy	$ 280,842	$ 270,524