Investments - Maturity Table (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Investments at cost	$ 196,402	$ 167,740
Mortgage-backed securities	195,391	$ 168,934
Maturity 2038
Schedule of Available-for-sale Securities [Line Items]
Investments at cost	284
Mortgage-backed securities	307
Maturity 2039
Schedule of Available-for-sale Securities [Line Items]
Investments at cost	7,539
Mortgage-backed securities	8,054
Maturity 2042
Schedule of Available-for-sale Securities [Line Items]
Investments at cost	22,336
Mortgage-backed securities	21,282
Maturity 2043
Schedule of Available-for-sale Securities [Line Items]
Investments at cost	59,961
Mortgage-backed securities	60,165
Maturity 2044
Schedule of Available-for-sale Securities [Line Items]
Investments at cost	47,833
Mortgage-backed securities	47,815
Maturity 2045
Schedule of Available-for-sale Securities [Line Items]
Investments at cost	58,449
Mortgage-backed securities	$ 57,768