Quarterly Financial Information (unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

The following table contains selected financial information from unaudited statements of income for each quarter of 2017 and 2016:

	Quarters Ended
	2017								2016
	Dec. 31 (a)		Sept. 30		June 30		Mar. 31		Dec. 31		Sept. 30		June 30		Mar. 31
Revenues	$	217,851	$	214,146	$	209,123	$	199,542	$	193,281	$	194,497	$	188,972	$	179,293
Gross profit	105,500		103,429		95,863		94,348		92,817		93,480		86,936		82,118
Income before income taxes	45,173		43,522		36,974		35,959		35,119		36,419		30,195		27,574
Net income	61,798		38,263		31,578		32,306		31,196		35,430		25,007		18,224
Earnings per diluted share	$	1.56	$	0.97	$	0.81	$	0.83	$	0.80	$	0.91	$	0.65	$	0.47
Shares used in computing diluted    earnings per share	39,499		39,342		39,201		38,932		38,975		39,062		38,738		39,071

(a) Fourth quarter 2017 includes the significant impact of the enactment of the Tax Act. The most significant impact of the Tax Act to us is the reduction in the U.S. federal corporate income tax rate from 35% to 21%.  The impact of the rate reduction on our 2017 income tax provision is a $21.6 million tax benefit due to the remeasurement of deferred tax assets and liabilities. Refer to Note 7 - "Income Tax" for further discussion on the impact the Tax Act.