Employee Benefits	12 Months Ended
Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Employee Benefits	8. Employee Benefits Defined Contribution Plans The Company sponsors defined contribution plans. The plans principally consist of contributory 401(k) savings plans and noncontributory profit sharing plans. The Company’s contributions to the 401(k) savings plans consist of a matching percentage. The Company match has historically been 50 percent of the first six percent of an eligible employee’s contributions. The Company’s total contributions to the 401(k) savings plans included in continuing operations for the years ended December 31, 2017, 2016 and 2015, were $8.3 million, $7.1 million, and $6.4 million, respectively. Deferred Compensation Plan The Capital Accumulation Plan is a nonqualified deferred compensation plan for Saia executives. The Capital Accumulation Plan allows for the plan participants to invest in the Company’s common stock. Elections to invest in the Company’s common stock are irrevocable and upon distribution, the funds invested in the Company’s common stock will be paid out in Company common stock rather than cash. At December 31, 2017 and 2016, the Company’s Rabbi Trust, which holds the investments for the Capital Accumulation Plan, held 170,310 and 166,807 shares of the Company’s common stock, respectively, all of which were purchased on the open market. The shares held by the Capital Accumulation Plan are treated similar to treasury shares and deducted from basic shares outstanding for purposes of calculating basic earnings per share. However, because the distributions are required to be made in Company stock, these shares are added back to basic shares outstanding for the purposes of calculating diluted earnings per share. Annual Incentive Awards The Company provides annual cash performance incentive awards to certain salaried employees which are based primarily on actual operating results achieved for the year, compared to targeted operating results. Operating results from continuing operations include performance incentive accruals of $12.2 million, $5.1 million, and $2.9 million in 2017, 2016 and 2015, respectively. Cash performance incentive awards for a year are primarily paid in the first quarter of the following year. Employee Stock Purchase Plan In January 2003, the Company adopted the Employee Stock Purchase Plan of Saia, Inc. (ESPP) allowing all eligible employees to purchase common stock of the Company at current market prices through payroll deductions of up to 10 percent of annual wages. In 2015, the Company amended the ESPP to allow highly compensated employees as defined by Section 401(a)(17) of the Internal Revenue Code to make payroll deductions of up to 20 percent of annual wages. The custodian uses the funds to purchase the Company’s common stock at current market prices. The custodian purchased 8,063, 20,532, and 7,327 shares in the open market during 2017, 2016 and 2015, respectively.

8. Employee Benefits

Defined Contribution Plans

The Company sponsors defined contribution plans. The plans principally consist of contributory 401(k) savings plans and noncontributory profit sharing plans. The Company’s contributions to the 401(k) savings plans consist of a matching percentage. The Company match has historically been 50 percent of the first six percent of an eligible employee’s contributions. The Company’s total contributions to the 401(k) savings plans included in continuing operations for the years ended December 31, 2017, 2016 and 2015, were $8.3 million, $7.1 million, and $6.4 million, respectively.

Deferred Compensation Plan

The Capital Accumulation Plan is a nonqualified deferred compensation plan for Saia executives. The Capital Accumulation Plan allows for the plan participants to invest in the Company’s common stock. Elections to invest in the Company’s common stock are irrevocable and upon distribution, the funds invested in the Company’s common stock will be paid out in Company common stock rather than cash. At December 31, 2017 and 2016, the Company’s Rabbi Trust, which holds the investments for the Capital Accumulation Plan, held 170,310 and 166,807 shares of the Company’s common stock, respectively, all of which were purchased on the open market. The shares held by the Capital Accumulation Plan are treated similar to treasury shares and deducted from basic shares outstanding for purposes of calculating basic earnings per share. However, because the distributions are required to be made in Company stock, these shares are added back to basic shares outstanding for the purposes of calculating diluted earnings per share.

Annual Incentive Awards

The Company provides annual cash performance incentive awards to certain salaried employees which are based primarily on actual operating results achieved for the year, compared to targeted operating results. Operating results from continuing operations include performance incentive accruals of $12.2 million, $5.1 million, and $2.9 million in 2017, 2016 and 2015, respectively. Cash performance incentive awards for a year are primarily paid in the first quarter of the following year.

Employee Stock Purchase Plan

In January 2003, the Company adopted the Employee Stock Purchase Plan of Saia, Inc. (ESPP) allowing all eligible employees to purchase common stock of the Company at current market prices through payroll deductions of up to 10 percent of annual wages. In 2015, the Company amended the ESPP to allow highly compensated employees as defined by Section 401(a)(17) of the Internal Revenue Code to make payroll deductions of up to 20 percent of annual wages. The custodian uses the funds to purchase the Company’s common stock at current market prices. The custodian purchased 8,063, 20,532, and 7,327 shares in the open market during 2017, 2016 and 2015, respectively.