Indebtedness - Revolving Credit and Term Loan Agreement (Details)			3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 18, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 17, 2017 USD ($)	Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items]
Principal balance on term loan	$ 372,691,000		$ 372,691,000		$ 372,691,000			$ 497,829,000
Repayments of long-term lines of credit					159,237,000	$ 206,455,000
Debt issuance costs expensed as interest expense for current period			4,707,000	$ 5,745,000	16,074,000	$ 17,961,000
Credit Facility
Line of Credit Facility [Line Items]
Line of credit, additional borrowing capacity		$ 250,000,000
Debt instrument, covenant compliance associated with additional borrowings, total debt to EBITDA		2.50
Debt instrument, covenant compliance, total debt to EBITDA		3.0
Debt instrument, covenant compliance, EBITDA plus lease expense to fixed charges		2.50
Debt issuance costs incurred in connection with debt agreement amendment		$ 2,800,000
Debt issuance costs expensed as interest expense for current period			200,000		200,000
Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity		400,000,000					$ 225,000,000
Principal balance on term loan	0		0		0			0
Long-term line of credit	400,000,000		400,000,000		400,000,000
Unamortized debt issuance costs deferred	3,300,000		3,300,000		3,300,000
Credit Facility | Letter of Credit
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity		$ 35,000,000					20,000,000
Credit Facility | Minimum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit, unused capacity, commitment fee percentage		0.15%
Credit Facility | Maximum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit, unused capacity, commitment fee percentage		0.30%
Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		1.25%
Credit Facility | London Interbank Offered Rate (LIBOR) | Maximum
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		2.25%
Credit Facility | Prime Rate | Minimum
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		0.25%
Credit Facility | Base Rate | Maximum
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		1.25%
Term Loan | Unsecured Debt
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity		$ 100,000,000						125,000,000.0
Line of credit, incremental increase to borrowing capacity		15,600,000
Principal balance on term loan	99,018,000		99,018,000		99,018,000		$ 84,400,000	94,626,000
Debt instrument, periodic payment		2,500,000
DAMI Credit Facility | Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Principal balance on term loan	0		0		0			$ 47,302,000
Repayments of long-term lines of credit	53,000,000
Unamortized debt issuance costs deferred	$ 1,400,000	$ 1,700,000	$ 1,400,000		$ 1,400,000