Supplemental Guarantor Financial Information - I/S (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Consolidating Statements of Comprehensive Income
Revenues	$ 309,822	$ 328,334	$ 323,961	$ 303,247	$ 303,304	$ 311,350	$ 303,746	$ 281,901	$ 1,265,364	$ 1,200,301	$ 1,054,821
Operating costs and expenses									1,118,985	1,060,384	950,182
Income from operations									146,379	139,917	104,639
Interest expense (income), net, including amortization of deferred financing costs and note discount									28,889	30,814	33,812
Redemption costs for early extinguishment of debt											9,075
Other (income) expense									2,958	3,780	(1,616)
Income before income taxes									114,532	105,323	63,368
Income tax (benefit) expense									26,622	39,342	28,174
Net income	24,959	27,478	20,114	15,359	14,823	21,644	14,740	14,774	87,910	65,981	35,194
Net loss attributable to noncontrolling interests									(81)	(1,099)	(1,946)
Net income attributable to controlling interests and available to common shareholders	$ 24,969	$ 27,490	$ 20,148	$ 15,384	$ 14,841	$ 22,009	$ 14,997	$ 15,233	87,991	67,080	37,140
Other comprehensive income (loss), attributable to controlling interest									(18,991)	(5,780)	(10,012)
Comprehensive income (loss) attributable to controlling interests									69,000	61,300	27,128
Consolidation Eliminations
Condensed Consolidating Statements of Comprehensive Income
Revenues									(10,973)	(11,025)	(11,155)
Operating costs and expenses									(10,973)	(11,013)	(11,228)
Income from operations										(12)	73
Equity in earnings of subsidiaries									269,912	66,188	59,604
Other (income) expense									29,329	13	(387)
Income before income taxes									(299,241)	(66,213)	(59,144)
Net income									(299,241)	(66,213)	(59,144)
Net loss attributable to noncontrolling interests									(81)	(1,099)	(1,946)
Net income attributable to controlling interests and available to common shareholders									(299,160)	(65,114)	(57,198)
Other comprehensive income (loss), attributable to controlling interest									20,323	5,119	10,052
Comprehensive income (loss) attributable to controlling interests									(278,837)	(59,995)	(47,146)
Parent
Condensed Consolidating Statements of Comprehensive Income
Operating costs and expenses									18,166
Income from operations									(18,166)
Equity in earnings of subsidiaries									(105,806)	(65,981)	(35,194)
Other (income) expense									263
Income before income taxes									87,377	65,981	35,194
Income tax (benefit) expense									(533)
Net income									87,910	65,981	35,194
Net income attributable to controlling interests and available to common shareholders									87,910	65,981	35,194
Other comprehensive income (loss), attributable to controlling interest									(18,991)	(5,780)	(10,012)
Comprehensive income (loss) attributable to controlling interests									68,919	60,201	25,182
Issuer
Condensed Consolidating Statements of Comprehensive Income
Operating costs and expenses									22,565	4,945	4,656
Income from operations									(22,565)	(4,945)	(4,656)
Interest expense (income), net, including amortization of deferred financing costs and note discount									25,188	22,633	21,749
Redemption costs for early extinguishment of debt											9,075
Equity in earnings of subsidiaries									(102,835)	964	(83,903)
Other (income) expense									(19,838)	(177)	(3,807)
Income before income taxes									74,920	(28,365)	52,230
Income tax (benefit) expense									(10,889)	(12,044)	(12,162)
Net income									85,809	(16,321)	64,392
Net income attributable to controlling interests and available to common shareholders									85,809	(16,321)	64,392
Other comprehensive income (loss), attributable to controlling interest									(8,793)	(10,404)	(4,582)
Comprehensive income (loss) attributable to controlling interests									77,016	(26,725)	59,810
Guarantors
Condensed Consolidating Statements of Comprehensive Income
Revenues									869,992	794,145	731,618
Operating costs and expenses									742,690	684,846	631,595
Income from operations									127,302	109,299	100,023
Interest expense (income), net, including amortization of deferred financing costs and note discount									30,804	5,650	10,352
Equity in earnings of subsidiaries									(61,271)	(1,171)	59,493
Other (income) expense									(11,271)	(4,073)	(6,060)
Income before income taxes									169,040	108,893	36,238
Income tax (benefit) expense									33,904	44,246	37,182
Net income									135,136	64,647	(944)
Net income attributable to controlling interests and available to common shareholders									135,136	64,647	(944)
Other comprehensive income (loss), attributable to controlling interest									(12,163)	14,632	9,688
Comprehensive income (loss) attributable to controlling interests									122,973	79,279	8,744
Non-Guarantors
Condensed Consolidating Statements of Comprehensive Income
Revenues									406,345	417,181	334,358
Operating costs and expenses									346,537	381,606	325,159
Income from operations									59,808	35,575	9,199
Interest expense (income), net, including amortization of deferred financing costs and note discount									(27,103)	2,531	1,711
Other (income) expense									4,475	8,017	8,638
Income before income taxes									82,436	25,027	(1,150)
Income tax (benefit) expense									4,140	7,140	3,154
Net income									78,296	17,887	(4,304)
Net income attributable to controlling interests and available to common shareholders									78,296	17,887	(4,304)
Other comprehensive income (loss), attributable to controlling interest									633	(9,347)	(15,158)
Comprehensive income (loss) attributable to controlling interests									$ 78,929	$ 8,540	$ (19,462)