Revenue Recognition - Cumulative Effect of Revenue Recognition Accounting Change (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 607,818	$ 519,431
Cost of operations	475,711	428,590
Operating Income	68,439	56,039
Provision for income taxes	20,715	10,771
Net income	34,122	$ 24,195
Current assets:
Contracts in progress	506,420		$ 621,411
Current liabilities:
Advance billings on contracts	40,207		32,252
Income taxes payable	40,670		34,562
Stockholders' equity:
Retained earnings (Accumulated deficit)	6,912		$ (48,221)
ASU 606 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	607,818
Cost of operations	475,711
Operating Income	68,439
Provision for income taxes	20,715
Net income	35,189
Current assets:
Contracts in progress	506,420
Current liabilities:
Advance billings on contracts	40,207
Income taxes payable	40,670
Stockholders' equity:
Retained earnings (Accumulated deficit)	6,912
ASU 606 [Member] | Legacy GAAP [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	590,307
Cost of operations	459,991
Operating Income	66,648
Provision for income taxes	19,979
Net income	34,134
Current assets:
Contracts in progress	493,750
Current liabilities:
Advance billings on contracts	49,310
Income taxes payable	39,934
Stockholders' equity:
Retained earnings (Accumulated deficit)	(14,125)
ASU 606 [Member] | Adjustment [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	17,511
Cost of operations	15,720
Operating Income	1,791
Provision for income taxes	736
Net income	1,055
Current assets:
Contracts in progress	12,670
Current liabilities:
Advance billings on contracts	(9,103)
Income taxes payable	736
Stockholders' equity:
Retained earnings (Accumulated deficit)	$ 21,037