Selected Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Quarterly Financial Data (Unaudited) [Abstract]
Revenues	$ 54,561	$ 53,898	$ 52,987	$ 50,959	$ 49,854	$ 44,939	$ 39,725	$ 39,407	$ 212,405	$ 173,925	$ 125,706
Operating expenses	27,770	27,695	25,144	23,111	20,268	18,893	15,363	16,515	103,720	71,039	47,681
Operating income	26,791	26,203	27,843	27,848	29,586	26,046	24,362	22,892	108,685	102,886	78,025
Net income attributable to CAI common stockholders	$ 15,591	$ 15,337	$ 16,931	$ 16,067	$ 17,411	$ 16,528	$ 15,135	$ 14,391	$ 63,926	$ 63,465	$ 50,189
Basic and diluted earnings per share available to CAI common stockholders [Abstract]
Basic (in dollars per share)	$ 0.70	$ 0.69	$ 0.76	$ 0.73	$ 0.87	$ 0.86	$ 0.78	$ 0.75	$ 2.89	$ 3.26	$ 2.60
Diluted (in dollars per share)	$ 0.69	$ 0.68	$ 0.75	$ 0.71	$ 0.85	$ 0.84	$ 0.77	$ 0.73	$ 2.82	$ 3.18	$ 2.55