Selected Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Quarterly Financial Data (Unaudited) [Abstract]
Revenues	$ 58,810	$ 59,203	$ 55,312	$ 54,264	$ 54,561	$ 53,898	$ 52,987	$ 50,959	$ 227,589	$ 212,405	$ 173,925
Operating expenses	31,575	32,024	30,968	29,835	27,770	27,695	25,144	23,111	124,402	103,720	71,039
Operating income	27,235	27,179	24,344	24,429	26,791	26,203	27,843	27,848	103,187	108,685	102,886
Net income attributable to CAI common stockholders	$ 16,162	$ 16,395	$ 13,446	$ 14,271	$ 15,591	$ 15,337	$ 16,931	$ 16,067	$ 60,274	$ 63,926	$ 63,465
Basic and diluted earnings per share available to CAI common stockholders [Abstract]
Basic (in dollars per share)	$ 0.78	$ 0.78	$ 0.61	$ 0.64	$ 0.70	$ 0.69	$ 0.76	$ 0.73	$ 2.91	$ 2.89	$ 3.26
Diluted (in dollars per share)	$ 0.76	$ 0.77	$ 0.60	$ 0.63	$ 0.69	$ 0.68	$ 0.75	$ 0.71	$ 2.85	$ 2.82	$ 3.18