Quarterly Financial Information - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 244,726	$ 240,135	$ 225,574	$ 209,997	$ 221,098	$ 225,103	$ 203,417	$ 190,968	$ 920,432	$ 840,586	$ 740,841
Cost of revenues	195,776	185,218	181,360	199,547	177,761	175,544	161,164	180,581	761,901	695,050	611,385
Gross margin	48,950	54,917	44,214	10,450	43,337	49,559	42,253	10,387	158,531	145,536	129,456
Net (loss) income	$ 10,486	$ 14,785	$ 11,126	$ (11,227)	$ 8,047	$ 10,233	$ 8,522	$ (8,003)	$ 25,170	$ 18,799	$ 25,494
Basic (loss) income per common share	$ 1.44	$ 2.03	$ 1.53	$ (1.55)	$ 1.11	$ 1.41	$ 1.18	$ (1.11)	$ 3.46	$ 2.60	$ 3.55
Diluted (loss) income per common share	$ 1.38	$ 1.96	$ 1.47	$ (1.55)	$ 1.08	$ 1.38	$ 1.16	$ (1.11)	$ 3.33	$ 2.55	$ 3.47