Debt - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended	6 Months Ended
	Apr. 30, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014
Line Of Credit Facility [Line Items]
Repayments of debt					$ 54,956,000	$ 2,017,000
Loss on early extinguishment of debt				$ 431,000	431,000
Loan outstanding balance		$ 239,251,000		337,722,000	337,722,000
Bank Line of Credit
Line Of Credit Facility [Line Items]
Line of credit facility, amount outstanding		48,597,000		140,024,000	$ 140,024,000
Bank Line of Credit | Credit Facility Agreements with Syndicate of Banks
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		50,000,000
Debt instrument maturity month and year					2016-12
Bank Line of Credit | Credit Facility Agreements with Syndicate of Banks | Letter of Credit Sub-Facility
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		1,000,000
Bank Line of Credit | Syndicated Working Capital Facility
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 205,000,000
Line of credit facility, borrowing capacity at closing date				187,000,000	$ 187,000,000
Line of credit facility, amount outstanding				80,000,000	80,000,000
Repayments of line of credit unpaid balance	49,700,000
Minimum unencumbered liquid assets to be maintained				$ 25,000,000	$ 25,000,000
Bank Line of Credit | Syndicated Working Capital Facility | Minimum
Line Of Credit Facility [Line Items]
Interest coverage ratio				200.00%	200.00%
Non Bank Term Loans
Line Of Credit Facility [Line Items]
Aggregate amount of debt			$ 119,500,000
Repayments of debt	3,500,000
Loss on early extinguishment of debt	$ 431,000
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		195,400,000
Debt maturity date					Dec. 31, 2021
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Senior Term Loan
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 158,500,000
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Senior Term Loan | LIBOR
Line Of Credit Facility [Line Items]
Debt instrument, variable rate periodic increase		0.25%
Debt instrument, variable rate		2.75%
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Subordinated Term Loan
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 24,000,000
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Subordinated Term Loan | Minimum
Line Of Credit Facility [Line Items]
Debt prepayment penalty percentage		0.00%
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Subordinated Term Loan | Minimum | LIBOR
Line Of Credit Facility [Line Items]
Debt instrument, variable rate		1.00%
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Subordinated Term Loan | Maximum
Line Of Credit Facility [Line Items]
Debt prepayment penalty percentage		2.00%
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Subordinated Term Loan | Maximum | LIBOR
Line Of Credit Facility [Line Items]
Debt instrument, variable rate		5.00%
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Working Capital Revolver Commitment
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		$ 5,000,000
Syndicated Term Loans | Credit Facility Agreements with Syndicate of Banks | Senior Secured Revolving Letter Of Credit Facility
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		7,900,000
Bank Term Loans
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity			38,000,000
Notes payable
Line Of Credit Facility [Line Items]
Proceeds from issuance of senior secured notes			$ 27,200,000
Notes payable | Payment in Kind ("PIK")
Line Of Credit Facility [Line Items]
Interest rate, stated percentage			12.00%
Loan outstanding balance		$ 2,900,000		$ 4,600,000	$ 4,600,000