Long-Term Obligations - Narrative (Details) - USD ($)			1 Months Ended		3 Months Ended	12 Months Ended			15 Months Ended	23 Months Ended
	Aug. 27, 2014	Jan. 24, 2012	Aug. 31, 2011	Aug. 31, 2010	Sep. 30, 2017	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2017	Aug. 27, 2019	Aug. 31, 2014	Apr. 30, 2013
Debt Instrument [Line Items]
Credit facility available				$ 600,000,000
Face amount of debt instrument			$ 581,300,000	500,000,000
Maximum borrowing capacity under credit agreement			125,000,000	100,000,000		$ 800,000,000
Financing costs incurred		$ 122,000	2,900,000	9,100,000		0	$ 7,987,000	$ 0
Debt retirement expenses recognized as part of income from continuing operations		47,000	865,000	2,100,000
Amount capitalized as deferred financing costs				$ 1,300,000
Proceeds from issuance of debt		50,000,000.0	100,000,000
Additional revolving commitment under new facility			25,000,000
Deferred charges		75,000	2,000,000
Write-off of previously capitalized deferred financing costs			$ 1,100,000
Increase in incremental facilities		50,000,000.0
Incremental facilities after amendment		$ 100,000,000.0
Deferred financing costs capitalized						6,133,000	7,874,000
Debt obligation						817,230,000	$ 735,230,000
Authorized share repurchase amount						$ 400,000,000					$ 400,000,000.0	$ 125,000,000.0
Voting equity guarantee on indebtedness, percentage						65.00%
Non-voting guarantee on indebtedness, percentage						100.00%
Covenant compliance, interest coverage ratio						20.57
Covenant terms, minimum interest coverage ratio						3
Covenant compliance, leverage ratio						2.07
Covenant terms, maximum leverage ratio						4.25
Senior Notes [Member]
Debt Instrument [Line Items]
Effective interest rate (percentage)						1.92%	1.67%
Debt obligation						$ 585,000,000	$ 600,000,000
Senior Notes [Member] | Forecast [Member]
Debt Instrument [Line Items]
Principal payment (quarterly)					$ 11,300,000				$ 7,500,000	$ 15,000,000
Senior Notes [Member] | Federal Funds Effective Swap Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate						0.50%
Senior Notes [Member] | Eurodollar [Member]
Debt Instrument [Line Items]
Basis spread on variable rate						1.00%
Credit Agreement [Member]
Debt Instrument [Line Items]
Financing costs incurred	$ 8,000,000
Write-off of previously capitalized deferred financing costs	200,000
Deferred financing costs capitalized	6,500,000
Debt related expense recognized as income from continuing operations	1,500,000
Credit Agreement [Member] | Base rate [Member] | Tier Four [Member]
Debt Instrument [Line Items]
Applicable margin for borrowings						0.50%
Credit Agreement [Member] | Eurodollar [Member] | Tier Four [Member]
Debt Instrument [Line Items]
Applicable margin for borrowings						1.50%
Credit Agreement [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit agreement	600,000,000
Senior Credit Facility [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit agreement	534,000,000
Secured debt [Member] | Credit Agreement [Member] | Line of credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit agreement	1,400,000,000.0
Revolving line of credit [Member]
Debt Instrument [Line Items]
Effective interest rate (percentage)						1.92%	1.67%
Debt obligation						$ 232,000,000	$ 135,000,000
Revolving line of credit [Member] | Credit Agreement [Member] | Line of credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit agreement	800,000,000
Revolving line of credit [Member] | Senior Credit Facility [Member] | Line of credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit agreement	125,000,000
Swing line [Member] | Credit Agreement [Member] | Line of credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit agreement	$ 25,000,000