Schedule I - Condensed Statements of Operations (Parent Company Only) (Detail) (USD $) In Thousands, 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
REVENUE
Total revenue									$ 2,363,017	$ 2,064,733	$ 1,994,013
OPERATING EXPENSES
Professional services									46,543	42,663	43,958
Other									39,983	80,258	38,099
Total operating expenses	434,347	452,499	467,916	426,220	539,536	399,236	449,467	380,306	1,780,982	1,768,545	1,788,563
NET INCOME	172,805	89,920	85,909	85,429	52,796	62,748	31,921	17,649	434,063	165,114	92,785
Parent Company [Member]
REVENUE
Equity in earnings of subsidiaries									373,713	103,769	20,598
Interest and other income									55,303	58,227	65,319
Total revenue									429,016	161,996	85,917
OPERATING EXPENSES
Professional services									1,594	1,662	1,477
Other									145	122	131
Total operating expenses									1,739	1,784	1,608
NET INCOME									$ 427,277	$ 160,212	$ 84,309