Fair Value Measurements - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Jun. 27, 2012	Aug. 25, 2010
Fair Value, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between measurement levels	$ 0	$ 0
Fair Value, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between measurement levels	0	0
Fair Value, Level 2 | $250 Million Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, fair value	273,000,000	267,700,000
Fair Value, Level 2 | $400 Million Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, fair value	430,400,000	432,000,000
Fair Value, Level 2 | Senior Notes | $250 Million Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, face amount				$ 250,000,000
Fair Value, Level 2 | Senior Notes | $400 Million Senior Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, face amount			$ 400,000,000
Fair Value, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between measurement levels	$ 0	$ 0