Fair Value Measurement (Quantitative Information Regarding Level 3 Valuations) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
AFS debt securities	$ 2,281,664	$ 2,288,785
Corporate debt, limited observable inputs | Level 3
Assets:
AFS debt securities	$ 3,440	5,079
Corporate debt, limited observable inputs | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Minimum
Assets:
Available-for-sale, measurement input	0.00
Corporate debt, limited observable inputs | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Maximum
Assets:
Available-for-sale, measurement input	0.05
Corporate debt, limited observable inputs | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Weighted average
Assets:
Available-for-sale, measurement input	0.025
Corporate debt, limited observable inputs | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Minimum
Assets:
Available-for-sale, measurement input	0.00
Corporate debt, limited observable inputs | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Maximum
Assets:
Available-for-sale, measurement input	0.05
Corporate debt, limited observable inputs | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Weighted average
Assets:
Available-for-sale, measurement input	0.025
Residential mortgage-backed and other commercial mortgage-backed securities | Level 3
Assets:
AFS debt securities	$ 1,298	0
Residential mortgage-backed and other commercial mortgage-backed securities | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Minimum
Assets:
Available-for-sale, measurement input	0.00
Residential mortgage-backed and other commercial mortgage-backed securities | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Maximum
Assets:
Available-for-sale, measurement input	0.05
Residential mortgage-backed and other commercial mortgage-backed securities | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Weighted average
Assets:
Available-for-sale, measurement input	0.025
Residential mortgage-backed and other commercial mortgage-backed securities | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Minimum
Assets:
Available-for-sale, measurement input	0.00
Residential mortgage-backed and other commercial mortgage-backed securities | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Maximum
Assets:
Available-for-sale, measurement input	0.05
Residential mortgage-backed and other commercial mortgage-backed securities | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Weighted average
Assets:
Available-for-sale, measurement input	0.025
Other asset-backed securities | Level 3
Assets:
AFS debt securities	$ 5,599	2,992
Other asset-backed securities | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Minimum
Assets:
Available-for-sale, measurement input	0.00
Other asset-backed securities | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Maximum
Assets:
Available-for-sale, measurement input	0.05
Other asset-backed securities | Level 3 | Measurement input, comparability adjustment | Market Comparable Securities | Weighted average
Assets:
Available-for-sale, measurement input	0.025
Other asset-backed securities | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Minimum
Assets:
Available-for-sale, measurement input	0.00
Other asset-backed securities | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Maximum
Assets:
Available-for-sale, measurement input	0.05
Other asset-backed securities | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Weighted average
Assets:
Available-for-sale, measurement input	0.025
Other investments | Level 3
Assets:
Assets measured at fair value	$ 1,338	$ 3,086
Other investments | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Minimum
Assets:
Other assets, measurement input	0.00%
Other investments | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Maximum
Assets:
Other assets, measurement input	10.00%
Other investments | Level 3 | Measurement input, comparability adjustment | Discounted Cash Flows | Weighted average
Assets:
Other assets, measurement input	5.00%