Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Investment Type Categorization [Domain]
Net unrealized gains (losses) on investments	$ 442,975		$ 349,910
Investment Type Categorization [Domain] | Other Long-term Investments [Member]
Net unrealized gains (losses) on investments	10,571		10,015
Investment Type Categorization [Domain] | Available-for-sale Securities [Member] | Fixed Maturities [Member]
Net unrealized gains (losses) on investments	389,787		322,358
Investment Type Categorization [Domain] | Available-for-sale Securities [Member] | Equity Securities [Member]
Net unrealized gains (losses) on investments	954		619
Securities Related to Other Than Temporary Impairments [Member] | Available-for-sale Securities [Member] | Fixed Maturities [Member]
Net unrealized gains (losses) on investments	5,382		5,333
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Investment Type Categorization [Domain]
Net unrealized gains (losses) on investments	$ 36,281	[1]	$ 11,585	[1]

[1] See Note 5 for more information on cash flow hedges.