Fair Value Measurements - Notes (Details) - Notes - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
2033 Senior Notes	$ 28,468	$ 24,647
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
2033 Senior Notes	28,468	24,647
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
2033 Senior Notes	$ 27,238	$ 25,676