Financial Commitments (Narrative) (Details)	3 Months Ended										6 Months Ended	12 Months Ended
	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2016	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Amended Credit Agreement [Abstract]
Operating Income (Loss)			$ 15,474,000	$ 38,974,000	$ 30,881,000	$ 20,084,000	$ 64,396,000	$ 70,354,000	$ 65,443,000	$ 41,497,000		$ 105,413,000	$ 241,690,000	$ 203,822,000
Loan outstanding			823,448,000				865,359,000					823,448,000	865,359,000
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Loan outstanding			823,448,000				865,359,000					823,448,000	865,359,000
Operating leases, rent expense
Operating leases, rent expense												17,400,000	24,400,000	$ 18,500,000
Senior Unsecured Notes [Member]
Senior Notes [Abstract]
Face amount			$ 300,000,000				300,000,000					$ 300,000,000	300,000,000
Interest rate (as a percent)			7.625%									7.625%
Net proceeds from the issuance, after discounts and issuance costs												$ 293,200,000
Redemption price												101.90%
Redemption price, change of control triggering event (as a percent)												101.00%
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Face amount			$ 300,000,000				300,000,000					$ 300,000,000	300,000,000
Amended Credit Agreement [Abstract]
Face amount			300,000,000				300,000,000					300,000,000	300,000,000
Loan outstanding			299,067,000				298,777,000					299,067,000	298,777,000
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Loan outstanding			299,067,000				298,777,000					299,067,000	298,777,000
Former Term Loan [Member]
Senior Notes [Abstract]
Face amount			200,000,000									200,000,000
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Face amount			200,000,000									200,000,000
Amended Credit Agreement [Abstract]
Face amount			200,000,000									200,000,000
Original Term Loan [Member]
Senior Notes [Abstract]
Face amount			250,000,000									250,000,000
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Face amount			250,000,000									250,000,000
2014			7,000,000									7,000,000
2015			19,000,000									19,000,000
2016			26,000,000									26,000,000
2017			34,000,000									34,000,000
2018			41,000,000									41,000,000
2019			123,000,000									123,000,000
Amended Credit Agreement [Abstract]
Face amount			250,000,000									250,000,000
Term Loan [Member]
Amended Credit Agreement [Abstract]
Loan outstanding			223,750,000				242,500,000					223,750,000	242,500,000
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Loan outstanding			223,750,000				242,500,000					223,750,000	242,500,000
Equipment Financing Loans [Member]
Amended Credit Agreement [Abstract]
Loan outstanding			70,600,000				102,000,000					70,600,000	102,000,000
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Loan outstanding			$ 70,600,000				102,000,000					$ 70,600,000	102,000,000
Term of debt												5 years
Transportation-Equipment Financing Loans [Member]
Senior Notes [Abstract]
Interest rate (as a percent)			3.35%									3.35%
Amended Credit Agreement [Abstract]
Loan outstanding			$ 45,000,000				40,600,000					$ 45,000,000	40,600,000
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Loan outstanding			45,000,000				40,600,000					$ 45,000,000	40,600,000
Term of debt												10 years
Transportation-Equipment Financing Loans Ballon Payment 2021 [Member]
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Balloon payments			12,400,000									$ 12,400,000
Transportation-Equipment Financing Loans Ballon Payment 2022 [Member]
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Balloon payments			6,150,000									6,150,000
Mortgages [Member]
Amended Credit Agreement [Abstract]
Loan outstanding			17,700,000				18,900,000					17,700,000	18,900,000
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Loan outstanding			17,700,000				18,900,000					$ 17,700,000	18,900,000
Term of debt												10 years
Mortgages Balloon Payment in 2016 [Member]
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Balloon payments			5,600,000									$ 5,600,000
Mortgages Balloon Payment in 2018 [Member]
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Balloon payments			2,600,000									2,600,000
Mortgages Balloon Payment in 2023 [Member]
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Balloon payments			$ 6,700,000									$ 6,700,000
Promissory Note [Member]
Senior Notes [Abstract]
Interest rate (as a percent)			5.00%									5.00%
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Promissory notes												$ 21,700,000
Minimum [Member] | Equipment Financing Loans [Member]
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Interest rate, minimum (as a percent)												2.12%
Maximum [Member] | Equipment Financing Loans [Member]
Equipment Financing, Mortgages And Acquisition-Related Notes [Abstract]
Interest rate, maximum (as a percent)												4.85%
Prime Rate [Member] | Mortgages [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												1.00%
LIBOR [Member] | Transportation-Equipment Financing Loans [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												3.00%
LIBOR [Member] | Mortgages [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												3.00%
LIBOR [Member] | Minimum [Member] | Original Term Loan [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												1.25%
LIBOR [Member] | Maximum [Member] | Original Term Loan [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												2.00%
Original Facility [Member]
Amended Credit Agreement [Abstract]
Revolver optional increase removed by amendment												$ 300,000,000
Percentage of foreign restricted subsidiary stock pledged as collateral												65.00%
Original Facility [Member] | Amendment Terms Based On Leverage Ratio Greater Than 3.5 to 1.0 [Member]
Amended Credit Agreement [Abstract]
Leverage ratio, Required												3.5
Maximum adjustment to Applicable Rate (as a percent)			1.00%									1.00%
Original Facility [Member] | Amendment Terms Based On Leverage Ratio Greater Than 4.0 to 1.0 [Member]
Amended Credit Agreement [Abstract]
Leverage ratio, Required												4.0
Maximum adjustment to Applicable Rate (as a percent)			1.00%									1.00%
Original Facility [Member] | Term Loan [Member]
Senior Notes [Abstract]
Face amount			$ 250,000,000									$ 250,000,000
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Face amount			250,000,000									250,000,000
Amended Credit Agreement [Abstract]
Face amount			250,000,000									$ 250,000,000
Original Facility [Member] | Minimum [Member]
Amended Credit Agreement [Abstract]
Fixed charge coverage ratio, Required												1.25
Original Facility [Member] | Minimum [Member] | Scenario, Plan [Member]
Amended Credit Agreement [Abstract]
Leverage ratio, Required	3.00
Original Facility [Member] | Maximum [Member] | Scenario, Plan [Member]
Amended Credit Agreement [Abstract]
Leverage ratio, Required	3.25	4.25									4.0
Former Revolver [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Maximum borrowing capacity			300,000,000									$ 300,000,000
Amended Credit Agreement [Abstract]
Maximum borrowing capacity			300,000,000									300,000,000
Original Revolver [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Maximum borrowing capacity			300,000,000									300,000,000
Amended Credit Agreement [Abstract]
Maximum borrowing capacity			300,000,000									300,000,000
Outstanding borrowings			158,000,000				130,000,000					158,000,000	130,000,000
Available borrowing capacity			141,800,000									$ 141,800,000
Original Revolver [Member] | Prime Rate [Member] | Minimum [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												1.25%
Original Revolver [Member] | Prime Rate [Member] | Maximum [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												2.00%
Original Revolver [Member] | LIBOR [Member] | Minimum [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												2.25%
Original Revolver [Member] | LIBOR [Member] | Maximum [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Basis points added to reference rate (as a percent)												3.00%
Letters Of Credit [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Maximum borrowing capacity			150,000,000									$ 150,000,000
Amended Credit Agreement [Abstract]
Maximum borrowing capacity			150,000,000									150,000,000
Letters of credit outstanding			200,000				$ 1,000,000					200,000	$ 1,000,000
Revolver [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Maximum borrowing capacity			300,000,000									300,000,000
Amended Credit Agreement [Abstract]
Maximum borrowing capacity			300,000,000									300,000,000
Swap [Member] | Original Facility [Member]
Credit Agreement - Revolving Credit Facility And Term Loan [Abstract]
Notional amount			$ 25,000,000									$ 25,000,000
Derivative, fixed interest rate			0.975%									0.975%
Brightwater Matter [Member]
Amended Credit Agreement [Abstract]
Pre-tax charge				$ 23,900,000
Brightwater Matter [Member] | Unfavorable Adjustments [Member]
Amended Credit Agreement [Abstract]
Operating Income (Loss)												$ (23,900,000)
Five Star Electric [Member] | Unfavorable Adjustments [Member]
Amended Credit Agreement [Abstract]
Operating Income (Loss)												$ (45,600,000)