Schedule I - Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Net cash flows provided (used) by operating activities	$ 99,471	$ 89,971	$ 44,201
Cash flows from investing activities:
Capital expenditures	92,644	44,221	34,475
Other assets	508	816	488
Net cash provided (used) by investing activities	(121,669)	(44,596)	(25,988)
Cash flows from financing activities:
Proceeds from short-term financing	11,192	6,775	4,585
Payments on short-term financing	7,584	4,950	3,781
Payments associated with induced conversion of 5.5% convertible debentures		558
Acquisition of 5.5% convertible debentures			(2,494)
Payments on loans secured by cash value of life insurance policies	1,918	84	380
Purchases of treasury stock			2,421
Proceeds from exercise of stock options	767	1,197	829
Excess income tax benefit associated with stock-based compensation	498	1,160	185
Acquisition of redeemable preferred stock	(39)
Dividends paid on preferred stocks	300	305	305
Net cash provided (used) by financing activities	(4,491)	12,891	(12,644)
Net increase (decrease) in cash and cash equivalents	(26,909)	57,983	5,207
Cash and cash equivalents at beginning of year	124,929	66,946	61,739
Cash and cash equivalents at end of year	98,020	124,929	66,946
Parent company [Member]
Condensed Financial Statements, Captions [Line Items]
Net cash flows provided (used) by operating activities	23,100	(5,558)	(3,074)
Cash flows from investing activities:
Capital expenditures			(51)
Payments received on note receivable from a subsidiary	10,000
Other assets	(266)	(283)	(439)
Net cash provided (used) by investing activities	9,734	(283)	(490)
Cash flows from financing activities:
Proceeds from short-term financing	11,192	6,775
Payments on short-term financing	(7,584)	(1,129)
Payments associated with induced conversion of 5.5% convertible debentures		(558)
Acquisition of 5.5% convertible debentures			(2,494)
Payments on loans secured by cash value of life insurance policies			(380)
Net change in due to/from subsidiaries	(50,460)	26,512	(7,430)
Purchases of treasury stock			(2,421)
Proceeds from exercise of stock options	767	1,197	829
Excess income tax benefit associated with stock-based compensation	498	1,160	185
Acquisition of redeemable preferred stock	(39)
Dividends paid on preferred stocks	(300)	(305)	(305)
Net cash provided (used) by financing activities	(45,926)	33,652	(12,016)
Net increase (decrease) in cash and cash equivalents	(13,092)	27,811	(15,580)
Cash and cash equivalents at beginning of year	35,302	7,491	23,071
Cash and cash equivalents at end of year	$ 22,210	$ 35,302	$ 7,491