Revenue Recognition - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue from Contract with Customer, Excluding Assessed Tax	$ 446,345	[1]	$ 399,537	$ 339,676	$ 345,611	$ 373,501	[1]	$ 373,502	$ 356,185	$ 300,129	$ 1,531,169	$ 1,403,317	$ 1,142,487
Contract with Customer, Liability, Revenue Recognized											22,100
Revenue, Remaining Performance Obligation	1,060,000										1,060,000
Retained Earnings (Accumulated Deficit)	$ 174,736					$ 143,241					174,736	$ 143,241
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue from Contract with Customer, Excluding Assessed Tax											$ 200
Retained Earnings (Accumulated Deficit)														$ 700

[1] Results for the fourth quarter of 2017 include a net 2017 Tax Act benefit of $7.8 million, or $0.48 and $0.47 per basic and diluted share, respectively.