SCHEDULE I - Parent Company Information - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 2,973	$ 2,577	$ (492)	$ 2,298	$ (277)	$ 979	$ 2,214	$ 4,331	$ 6,553	$ (2,229)	$ 9,692	$ 1,610	$ 7,356	$ 7,247	$ 15,626
Adjustments to reconcile net income to net cash provided by operating activities:
Write-down of equipment													9,181	5,602	6,461
Stock-based compensation expenses													4,150	3,509	3,439
Amortization of deferred costs													4,307	4,319	4,113
Amortization of interest rate derivative cost														(499)	(404)
Allowances and provisions													697	(81)	(684)
Gain on sale of leased equipment													(8,354)	(5,753)	(5,675)
Gain on insurance settlement															(351)
Income from joint ventures													(1,175)	(1,329)	(3,526)
Deferred income taxes													6,508	3,996	(4,389)
Changes in assets and liabilities:
Receivables													(5,857)	4,454	2,269
Spare parts inventory													(4,128)	5,964
Other assets													(2,635)	(590)	(3,158)
Accounts payable and accrued expenses													1,669	(1,881)	(23)
Maintenance reserves													4,580	(10,861)	14,022
Security deposits													5,747	1,159	614
Unearned lease revenue													748	793	(1,064)
Net cash provided by operating activities													109,121	62,731	80,296
Cash flows from investing activities:
Proceeds from sale of equipment held for operating lease (net of selling expenses)													45,701	43,632	38,706
Capital contribution to joint ventures													(630)	(17,623)	(11,219)
Distributions received from joint venture													1,304	847
Acquisitions of J.T. Power, net of cash acquired															(4,171)
Investment in WOLF, net of cash acquired															2,020
Purchase of equipment held for operating lease													(183,616)	(128,075)	(136,231)
Purchase of property, equipment and furnishings													(3,988)	(13,831)	(453)
Net cash used in investing activities													(157,992)	(108,684)	(131,850)
Cash flows from financing activities:
Proceeds from issuance of notes payable													192,700	154,395	130,000
Debt issuance cost													(13)	(5,074)	(1,252)
Proceeds from shares issued under stock compensation plans													518	410	680
Cancellation of restricted stock units in satisfaction of withholding tax													(1,558)	(1,544)	(1,248)
Security deposit													(1,606)	4,553	7,588
Repurchase of common stock													(16,500)	(5,352)	(5,918)
Excess tax benefit from stock-based compensation													26	311
Principal payments on notes payable													(153,816)	(101,054)	(70,874)
Net cash provided by (used in) financing activities													45,110	46,645	58,976
Increase/(Decrease) in cash and cash equivalents													(3,761)	692	7,422
Cash and cash equivalents at beginning of period				13,493				12,801				5,379	13,493	12,801	5,379
Cash and cash equivalents at end of period	9,732				13,493				12,801				9,732	13,493	12,801
Net cash paid for:
Interest													35,568	33,132	33,931
Income Taxes													353	210	111
Supplemental disclosures of non-cash investing activities:
Engines and equipment, transferred from Held for Operating Lease to Held for Sale but not settled													22,079	3,071	15,166
Engines and equipment, transferred to (from) the parent to its subsidiaries													41,410
Equipment Held For Sale Transfer To Spare Parts Inventory													6,061	9,649
Parent Company
Cash flows from operating activities:
Net income													7,356	7,247	15,626
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in income of subsidiaries													(7,778)	(7,736)	(19,760)
Depreciation expense													40,867	29,555	19,699
Write-down of equipment													6,764	4,681	4,204
Stock-based compensation expenses													4,150	3,509	3,439
Amortization of deferred costs													2,646	2,391	2,286
Amortization of interest rate derivative cost														(499)	(404)
Allowances and provisions													(17)	34	(94)
Gain on sale of leased equipment													(2,488)	(2,147)	(3,472)
Gain on insurance settlement															(351)
Income from joint ventures													(1,175)	(1,329)	(3,526)
Deferred income taxes													2,287	1,383	(4,072)
Changes in assets and liabilities:
Receivables													(953)	(1,502)	1,871
Spare parts inventory													4,847	(5,533)
Other assets													(2,420)	(942)	(2,165)
Accounts payable and accrued expenses													4,589	322	(943)
Due to / from subsidiaries													1	(2,208)	(4,041)
Maintenance reserves													5,227	8,693	3,495
Security deposits													5,254	(1,616)	426
Unearned lease revenue													646	919	(575)
Net cash provided by operating activities													69,803	35,222	11,643
Cash flows from investing activities:
Increase in investment in subsidiaries													(23,923)	(9,666)	(34,098)
Distributions received from subsidiaries													3,791	17,582	69,548
Proceeds from sale of equipment held for operating lease (net of selling expenses)													22,885	21,360	21,644
Capital contribution to joint ventures													(630)	(17,623)	(11,219)
Distributions received from joint venture													1,304	847
Acquisitions of J.T. Power, net of cash acquired															(4,171)
Investment in WOLF, net of cash acquired															(1,000)
Purchase of equipment held for operating lease													(170,732)	(104,904)	(132,140)
Purchase of property, equipment and furnishings													(3,736)	(13,767)	(450)
Net cash used in investing activities													(171,041)	(106,171)	(91,886)
Cash flows from financing activities:
Proceeds from issuance of notes payable													192,700	154,395	130,000
Debt issuance cost													(13)	(5,074)	(637)
Proceeds from shares issued under stock compensation plans													518	410	680
Cancellation of restricted stock units in satisfaction of withholding tax													(1,558)	(1,544)	(1,248)
Security deposit													(1,606)	4,553	7,588
Repurchase of common stock													(16,500)	(5,352)	(5,918)
Excess tax benefit from stock-based compensation													26	311
Principal payments on notes payable													(71,846)	(75,859)	(52,844)
Net cash provided by (used in) financing activities													101,721	71,840	77,621
Increase/(Decrease) in cash and cash equivalents													483	891	(2,622)
Cash and cash equivalents at beginning of period				$ 2,411				$ 1,520				$ 4,142	2,411	1,520	4,142
Cash and cash equivalents at end of period	$ 2,894				$ 2,411				$ 1,520				2,894	2,411	1,520
Net cash paid for:
Interest													16,462	11,110	11,903
Income Taxes													75	76	111
Supplemental disclosures of non-cash investing activities:
Engines and equipment, transferred from Held for Operating Lease to Held for Sale but not settled													$ 21,786	3,071	422
Engines and equipment, transferred to (from) the parent to its subsidiaries														$ 120,880	$ 116,020