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Notes Payable - Additional Information (Detail) - USD ($) |  |  | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Nov. 05, 2015 | Mar. 17, 2014 | Dec. 31, 2016 | Mar. 31, 2016 | Feb. 09, 2016 | Dec. 31, 2015 | Apr. 21, 2011
Debt Instrument [Line Items] |  |  |  |  |  |  |
Consolidated Fixed Charge Coverage Ratio |  |  | 2.50% |  |  |  |
Consolidated Fixed Charge Coverage Ratio, actual |  |  | 3.74% |  |  |  |
Consolidated Leverage Ratio |  |  | 2.75% |  |  |  |
Consolidated Leverage Ratio, actual |  |  | 2.00% |  |  |  |
Line of credit facility covenants tangible net worth description |  |  | Permit Tangible Net Worth, calculated as of the last day of each fiscal quarter, to be less than the sum of (i) $229.0 million, plus (ii) 25% of net income for such fiscal quarter subsequent to December 31, 2010, plus (iii) 90% of the net cash proceeds from the issuance of the Company’s capital stock after December 31, 2010. |  |  |  |
Tangible Net Worth sum |  |  | $ 313,300,000 |  |  |  |
Consolidated Net Income |  |  | 25.00% |  |  |  |
Percentage of net cash proceeds from issuance of capital stock |  |  | 90.00% |  |  |  |
Actual tangible net worth |  |  | $ 357,900,000 |  |  |  |
Senior notes principal balance outstanding |  |  | $ 326,376,000 |  |  | $ 381,441,000 |
2016 Amendment [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Senior notes description |  |  | (i) the issuance period for the shelf notes to be issued and sold pursuant to the Note Purchase Agreement is extended until the earlier of February 9, 2019 or the termination of the issuance and sale of the shelf notes upon the 30 days’ prior notice of either PIM or the Company, and (ii) the definition of the “Available Facility Amount,” which is the aggregate amount of the shelf notes that may be authorized for purchase pursuant to the Note Purchase Agreement was amended to equal a formula based on: $250 million, minus the aggregate principal amount of the shelf notes then outstanding and purchased pursuant to the Note Purchase Agreement, minus the shelf notes accepted by the Company for purchase, but not yet purchased, by the Purchaser pursuant to the Note Purchase Agreement; provided, however, the aggregate amount of the shelf notes purchased by any corporation or other entity controlling, controlled by, or under common control with, PIM shall not exceed $200 million. |  |  |  |
Stated formula value for determining available facility amount |  |  |  |  | $ 250,000,000 |  |
Series A senior notes [Member] | 4.03% Series A senior notes due in 2018 [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  | $ 100,000,000
Senior notes interest rate |  |  | 4.03% |  |  |  | 4.03%
Debt instrument, payment terms |  |  | Interest on these notes is due semi-annually in arrears and the principal is due in five equal annual installments, with the first payment due on April 21, 2014. |  |  |  |
Debt instrument, maturity date |  |  | Apr. 21, 2018 |  |  |  |
Debt instrument, date of first required payment |  |  | Apr. 21, 2014 |  |  |  |
Senior notes principal balance outstanding |  |  | $ 40,000,000 |  |  | 60,000,000 |
Series B Senior Notes | 3.68% Series B senior notes due in 2021 [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Senior notes interest rate |  | 3.68% | 3.68% |  |  |  |
Debt instrument, maturity date |  |  | Mar. 17, 2021 |  |  |  |
Senior notes principal balance outstanding |  |  | $ 40,000,000 |  |  | 40,000,000 |
Proceeds from issuance of senior notes |  | $ 40,000,000 |  |  |  |  |
Senior notes description |  |  | The Series B Senior Notes are an unsecured obligation of the Company, bear interest at a rate of 3.68% per annum and mature on March 17, 2021. Interest on the Series B Senior Notes is payable semi-annually beginning on September 17, 2014 and continuing thereafter on March 17 and September 17 of each year until maturity. |  |  |  |
Senior notes interest payment |  |  | Semi-annually |  |  |  |
Series C Senior Notes | 3.84% Series C senior notes due in 2022 [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Senior notes interest rate | 3.84% |  | 3.84% |  |  |  |
Debt instrument, payment terms |  |  | Interest on the Series C Senior Notes is payable semi-annually beginning on May 5, 2016 and continuing thereafter on November 5 and May 5 of each year until maturity. |  |  |  |
Debt instrument, maturity date |  |  | Nov. 05, 2022 |  |  |  |
Debt instrument, date of first required payment |  |  | May 05, 2016 |  |  |  |
Senior notes principal balance outstanding |  |  | $ 60,000,000 |  |  | $ 60,000,000 |
Proceeds from issuance of senior notes | $ 60,000,000 |  |  |  |  |  |
Senior notes interest payment |  |  | Semi-annually |  |  |  |
Minimum [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Tangible Net Worth sum |  |  | $ 229,000,000 |  |  |  |
Maximum [Member] | 2016 Amendment [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  | $ 200,000,000 |  |
Credit Facility [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Revolving credit facility, maturity period |  |  | 5 years |  |  |  |
Revolving credit facility, maturity date |  |  | Mar. 31, 2021 |  |  |  |
Credit facility, maximum |  |  | $ 420,000,000 |  |  |  |
Revolving credit facility, available maximum borrowing capacity |  |  | 620,000,000 |  |  |  |
Additional commitments |  |  | $ 200,000,000 |  |  |  |
Consolidated Fixed Charge Coverage Ratio |  |  | 2.50% |  |  |  |
Consolidated Fixed Charge Coverage Ratio, actual |  |  | 3.74% |  |  |  |
Consolidated Leverage Ratio |  |  | 2.75% |  |  |  |
Consolidated Leverage Ratio, actual |  |  | 2.00% |  |  |  |
Line of credit facility covenants tangible net worth description |  |  | Permit Tangible Net Worth as of the end of any fiscal quarter of the Company to be less than the sum of (i) $246.1 million plus (ii) 25% of the Company’s Consolidated Net Income (as defined in the Amended Credit Facility) (but only if a positive number) for each fiscal quarter ended subsequent to December 31, 2011 |  |  |  |
Tangible Net Worth sum |  |  | $ 313,300,000 |  |  |  |
Consolidated Net Income |  |  | 25.00% |  |  |  |
Percentage of net cash proceeds from issuance of capital stock |  |  | 90.00% |  |  |  |
Actual tangible net worth |  |  | $ 357,900,000 |  |  |  |
Debt instrument description of variable rate basis |  |  | (i) LIBOR plus a defined margin, or (ii) the Agent bank’s prime rate (“base rate”) plus a margin. The applicable margin for each type of loan is measured based upon the Consolidated Leverage Ratio at the end of the prior fiscal quarter and ranges from 1.00% to 1.75% for LIBOR loans and 0% to 0.75% for base rate loans. In addition, the Company pays an unused commitment fee for the portion of the $420.0 million credit facility that is not used. These fees are based upon the Consolidated Leverage Ratio and range from 0.15% to 0.30%. As of December 31, 2016 and 2015, the applicable margins were 1.50% and 1.75% for LIBOR based loans, respectively, 0.50% and 0.75% for base rate loans, respectively and 0.25% and 0.30% for unused fees, respectively. Amounts borrowed under the Sweep Service Facility are based upon the MUFG Union Bank, N.A. base rate plus an applicable margin and an unused commitment fee for the portion of the $12.0 million facility not used. |  |  |  |
Unused commitment fees |  |  | $ 420,000,000 |  |  |  |
Credit Facility [Member] | Unused Fees [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt instrument interest rate at period end |  |  | 0.25% |  |  | 0.30% |
Credit Facility [Member] | LIBOR Loans [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt instrument interest rate at period end |  |  | 1.50% |  |  | 1.75% |
Credit Facility [Member] | Base Rate Loans [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt instrument interest rate at period end |  |  | 0.50% |  |  | 0.75% |
Credit Facility [Member] | Sweep Service Facility [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Credit facility, maximum |  |  | $ 432,000,000 |  |  |  |
Revolving credit facility, available maximum borrowing capacity |  |  | 245,600,000 |  |  |  |
Amount outstanding |  |  | 186,400,000 |  |  |  |
Unused commitment fees |  |  | 12,000,000 |  |  |  |
Credit Facility [Member] | Minimum [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Tangible Net Worth sum |  |  | $ 246,100,000 |  |  |  |
Leverage ratio |  |  | 0.15% |  |  |  |
Credit Facility [Member] | Minimum [Member] | LIBOR Loans [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Leverage ratio |  |  | 1.00% |  |  |  |
Credit Facility [Member] | Minimum [Member] | Base Rate Loans [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Leverage ratio |  |  | 0.00% |  |  |  |
Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Leverage ratio |  |  | 0.30% |  |  |  |
Credit Facility [Member] | Maximum [Member] | LIBOR Loans [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Leverage ratio |  |  | 1.75% |  |  |  |
Credit Facility [Member] | Maximum [Member] | Base Rate Loans [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Leverage ratio |  |  | 0.75% |  |  |  |
Unsecured revolving credit facility before Renewal [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Credit facility, maximum |  |  | $ 420,000,000 |  |  |  |
Letters of Credit [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Credit facility, maximum |  |  | 25,000,000 |  |  |  |
Letters of Credit [Member] | Minimum [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Credit facility, maximum |  |  |  | $ 10,000,000 |  |  |
Letters of Credit [Member] | Maximum [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Credit facility, maximum |  |  |  | $ 12,000,000 |  |  |
Swingline Loans [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Credit facility, maximum |  |  | $ 10,000,000 |  |  |  |

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The cash inflow associated with the sale of a borrowing supported by a written promise to pay an obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585 + Details
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