Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information

	2017								2016
	1Q		2Q		3Q		4Q		1Q (1)		2Q		3Q		4Q
Contract revenue	$	296,295	$	306,392	$	305,301	$	321,174	$	283,599	$	305,419	$	306,520	$	289,559
Operating income	$	16,633	$	22,208	$	23,396	$	20,181	$	17,694	$	19,358	$	23,776	$	21,965
Net income	$	10,177	$	11,937	$	13,692	$	27,070	$	9,891	$	10,583	$	13,437	$	12,673
Earnings per share:
Basic	$	0.54	$	0.64	$	0.73	$	1.45	$	0.52	$	0.56	$	0.71	$	0.67
Diluted	$	0.52	$	0.63	$	0.72	$	1.41	$	0.51	$	0.55	$	0.70	$	0.65
Weighted-average common shares outstanding (in thousands)
Basic		18,972		18,775		18,666		18,646		18,994		19,008		18,965		18,988
Diluted		19,423		19,086		19,024		19,136		19,273		19,293		19,329		19,512