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Investments - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Other investments, at cost $ 24,222 $ 14,840
Maximum percentage of shareholders' equity security holdings held of one issuer 10.00% 10.00%
Available-for-sale securities pledged as collateral, fair value $ 466,100 $ 407,300
Mortgage-backed securities, weighted average life 5 years